At the moment, I'm just wondering if anyone knows of any low-hanging fruit, so to speak. Basically, is there some winetrick that improves performance significantly, for example.

(For the record, the CPU is an AMD Ryzen 3500U, and the GPU is integrated (Vega 8, I believe).)

Unfortunatelly, unless you want comically long list, your description is way too superficial.
There is nothing I can toss you for starters as the issue could be caused by like a billion of various things.
Without solid specifics there isn't much of troubleshooting unless you like wasting time for testing totally random stuff with correlation to nothing (because with this level of details that's about all that can be given to you).

Could you maybe ask a question that might help troubleshooting this?

Edit: I'd also like any advice that you would give in almost all circumstances.

I may potentially be overspecialized and potentially couldn't give "general" advices.
If I would start to give you any I would likely send you on a venture of disecting your entire system.

I can give you some questions to get the general idea what is the magnitude of the problem and potential complexity of the solution.

Tho the first thing I'm going to ask is this:
-1. how urgent is this? Do you want this done within a week or can you afford stretching it into 1-2 months?
This is a serious question as I am going through many depths of hell in my IRL life atm (I was before, and over time it's only getting worse so far) and so I will definitely not be able to help you troubleshoot this within a singular week if the issue is too complex.

So:
0. driver type, mesa or something official, if official then what exactly (there are few different official amd drivers)
1. what are you using for vulkan, is it radv or amdvlk (or else)
2. dxvk version
3. define "performance issues", what is it? Stuttering? More non-spike fps drops? More noticable fps drops in specific situations?
4. when was the last time you updated your gpu driver in relation to when the problem started occuring (this is related to shader cache which gets rebuild from scratch after each mesa update)
5. storage device used (hdd, ssd, others, depending on what it is and what else loads it during gameplay it could potentially be a bottleneck during new areas load-in causing issues)
6. amount of ram available total in system
7. when you start the game how much ram do you have free on average (real free, after accounting for buffers and cache)
8. cpu performance governor used during game
9. do you use p states on the cpu
10. do you use SMT on the cpu
11. do you use dynamic boost frequency on the cpu
12. did you try running just the game and nothing else at the time, if so did the issue persist
13. do you use compositor (in DE / WM), if yes then do you run it while playing the game
14. x11 or wayland? Or xwayland?
15. did you change nice level of literally anything
16. what audio backend do you use: pulseaudio, alsa, jack, jack2, oss, other ones
17. did you change your audio backend settings
18. do you use realtime kernel patches
19. mouse polling rate (yes, this is rather major issue, tho wine devs appear to ALWAYS deny that it's de facto THEIR code's issue and refuse to fix the related thing)
20. do you use freesync with the game
21. do you use multi-head (multiple screens)
22. this is a laptop I presume? (mobile chip itself doesn't warrant that as there are some IoT boards with these) Do you have issues with cooling by any chance?
23. do you play the game with psu connected
24. is the issue consistent over time or does it get worse during prologned gameplay sessions and / or long system uptime
25. do you have swap, if yes then how much, what type (file, partition)
26. do you use disk encryption
27. do you use file indexing on the system
28. do you have any cron / scheduled jobs
29. file system used on the drive hosting the game, and did you use any non default mount flags in fstab
30. has the issue always been there or did it start recently
31. are you connected to any networks during the gameplay
32. when the issue happens does the audio get out of sync or not

This is for starters. As I said with such low amount of info I could give you comically long troubleshooting list, with this above not being even a "start" of it.

No, it's not urgent.

(The game still runs, and it runs properly; it's just that it runs rather slowly in certain circumstances.)

Noticeable FPS drops. Specifically, when exploring M.o.Metal (the first area of the game):
* On the surface, there is a major FPS drop. (Note that this greatly slows down movement, as the game doesn't skip frames; if it did skip frames, the FPS drop wouldn't be an issue.)
* Underground, there is a FPS drop, but not as severe.
* In town, and during battle, the game runs at full speed, so no issue.
* For cutscenes, it only runs slow if the actual first person dungeon view is displayed; fortunately, often cutscenes use a different background, and the issue isn't present there.

X11 with fluxbox, so I believe no compositor.

Yes, except that I use arandr to disable the integrated screen and only use an external monitor. (I have not tried it on the integrated screen.)

Sometimes, but I don't notice a difference.

(On the other hand, for a different game, Bloodstained, I do notice a difference; the game runs slowly on battery power (unless I resume from suspend-to-RAM while on battery power), but runs just fine with the AC adapter connected, aside from stuttering when the game loads new objects.)

It's consistent over time.
No audio desync. (In particular, I can still rely on audio cues to know when an auto-move has finished or an encounter has started.)

What's freesync?

Usually ondemand, and I tried performance and it didn't seem to make a difference. (I highly doubt that powersave would help, as I don't think this would be a cooling issue.)

No (or at least not conciously); how does that work, and how would I do that?

(By the way, if you're wondering where I'd prefer you to spend any time you choose to spend helping me, I would prefer it to be spent on the questions I post in response to yours.)

How did you install WINE and DXVK?
Debian testing only provides WINE 5.0.3, but current DXVK 1.8.1 requires WINE ≥ 5.8.

I'm busy now. I'll respond later.

And who is forcing him/her to run the latest version?
At the very least DXVK's github repo has older builds available.
Either way it's totally possible to install non-current ones.

WINE was installed through apt.

DXVK was installed via winetricks, which itself was installed through apt.

(Only the official debian repository is present on this system.)

As far as the idea of trying out a newer version:
* Has there been at least one change that would likely result in a performance improvement here?
* What's the best way to install a newer version without it polluting the main system? (In particular, I don't want to add any more debian repositories. I have used chroot in the past, is that a good option, and if so, what's the best distro to run in the chroot for this purpose? Or does it make sense to just compile it myself in my home directory? There's also the issue of managing the wine prefix.)

This is the part I do not understand. The version of winetricks provided by Debian testing repositories installs DXVK 1.8.1, but this one requires WINE ≥ 5.8.

Did you not get an error about versions incompatibility during DXVK installation in the WINE prefix?

---

By the way, is this the game you have issues with?

On GOG requirements list, it is advertised as using OpenGL rendering, not Direct3D. So DXVK would probably have no effect at all with this game.

Yes.

Then, as I posted earlier, I do not think DXVK is a good track to follow to improve the game performances.
At least not until you can make sure that:
- the game runs with Direct3D 9 to 12, despite what is shown on the GOG store page
- DXVK is working well on Debian Bullseye, despite the error shown by winetricks when installing it

If the Wine version is truly 5.0.3 then that's really ancient and there've been hundreds of patches to Wine since then.

You could try updating your Wine, and also DXVK for good measure, but like vv221 said, DXVK does nothing with OpenGL games.

It's difficult to say what could be the performance issue - an integrated GPU on OpenGL doesn't exactly help. I wonder if you had similarly poor performance on Windows too, meaning no amount of Linux tweaking would help.

Still, update Wine and see what happens. THere should be instructions for Debian out there. I use Arch and custom Wine from TkG, so can't really help in that department much.

Installing DXVK did improve Bloodstained. (I don't know what version is installed.)