Just in case someone is coming from the reviews at the store page, the issues with the DLC requiring Galaxy to be running have been fixed.

Official feedback was given here:
https://www.gog.com/forum/general/dungeon_siege_and_deus_ex_series_now_available_on_gogcom_f6c95/post612

Tested with the updated offline installers and all DLC is now properly working without Galaxy, as it should be. Other users reported the same in this thread: https://www.gog.com/forum/deus_ex_mankind_divided/game_is_missing_the_outfitweapon_dlcs

I just finish download the season pass fix but it doesn't work with the base game, I have to download everything again and that's a real problem bacause internet runs like shit lately, can you confirm that the dlc work without internet and GOG Galaxy activated?

This is good to hear. What about those 'one time' bonuses, the praxis kits and the credits? Are those once per save, per install, just period? Do we even get them at all?

What problem did you have? It's included in the description so I guess it has been fixed, if I could test I would answer your cuestion but I guess is one per save... The Covert Agent Pack it's included in every playthrough, at least on Playstation, and in this version is part of the Covert Agent...

The DLC DRM

Just finished testing the game and almost every DLC is available except the Augmented Covert Agent Pack and the one time consumable items, it's not available ingame I will try again or I would try to contact support center

It's already solved, in most part, try download the hotfix, I can confirm that using the offline installer without being online I have access to the assault pack, the stealth pack, Story DLC and Outfits, Augmented Cover Agent Pack is absent

Yeah it seems to be working for me ass well. How do you access the assault pack and stealth pack? I don't want to start the game just yet but I do want to make sure it is all working.

Open the menu while playing and select inventory, switch to the storage and there you find all the weapons, but no items

As expected, the one and only thing that has been changed in hotfix is ghost_api64.dll.
I'm still replacing GOG hotfix with PLAZA DXMD.exe/steam_api64.dll/steam_emu.ini, since their wrapper is better than this one from GOG. When Galaxy is not installed and game is truly offline (internet cable unplugged) - initial startup time (as, for example, in Bioshock) are 10-15 sec longer with GOG 1.19 (with or without hotfix), PLAZA wrapper starts straight away. And yes, it's the same thing:
As PLAZA said, GOG was given DRM free (no Denuvo) Steam version of game exe and they essentially HEX replaced "steam" strings in exe with "ghost" and steam_api64.dll with ghost_api64.dll. Sad for GOG, their ghost_api64.dll in first release did not unlock DLCs properly. What PLAZA did was just reversing GOG process of converting steam exe to GOG.
Unfortunately, GOG does not care about their wrapper/emu being fast and efficient, that 10-15 sec longer startup times are probably from checking if Galaxy / internet connection are available.

Well keep in mind that GoG 1.19 is heavy outdated by now, so no wonder the wrapper causes
trouble... last "old" Galaxy version is now on 1.2611 someting something.

Did run in no trouble with the game on Galaxy 2.0 even without the "hotfix" everything did
run standalone for me, not sure why it bugged out for others.

Emm, are you aware that the problem was, precisely, having "galaxy drm"? Of course it all ran for you, because you were using Galaxy and so you passed the check. It has nothing to do with the version, but with needing the launcher to run the game. The difference in time starting the game without the launcher has nothing to do, also, with the launcher version, but with the wrapper-bypass that in the case of GOG still does a check to see if Galaxy is running, as @kingit explained.

This is all about game not having ANY drm check, as it should be. Maybe you did not understand what was the problem here if you did not understand also why "it bugged out" for us to have a GOG game with any kind of drm in it.

I test EVERY game i purchase for complete and 100% standalone fucntionality.
DE MD did ran for me WITHOUT GALAXY running and WITHOUT internetconnection.
Also without the communication service running in the background.

THE GAME worked STANDALONE completely even before the fix was done, yes also
the DLC.

Hope that clarifies what i meant, i test EVERY game for that functionality. Ever since i buy
GoG exclusively. I don t know why ppl insist GoG uses a "hidden" DRM tech. They use
datacollecting tech as every other platform out there. But the games work and will work
without Galaxy running and even when the communication service is killed.

once more to make it VISIBLE what i mean:

I TEST EVERY GAME on purchase for:

1 running WITHOUT the launcher called GALAXY
2 running WITHOUT internet connection
3 running WITHOUT and GoG services in the background

and the games WORK as DE MD did and DOES work WITHOUT all that up and running.
On the day i purchased, so yes i believe you guys that the game did that, but it was a bug
not a hidden DRM tech, or the staff trying to push something like this. The whole reason
why this platform exist is selling games without DRM.

No, it did not. It was broken for EVERYONE. If it did work as intended, there would be no SCENE RELEASE for a GOG game for the first time, ever.