You should probably decide on size at this point as it will affect a lot of things.

You can use a B450 motherboard if you can update the UEFI ("BIOS") to work with your newer chip as with that processor, motherboard and SSD it matters not that is does not support PCIe 4.0. Those can be had cheap now.

I could write more but falling asleep here.

How can I update the BIOS if I don't have a CPU that's supported pre-update?

Not supported at all? Or certain features aren't supported? Hard to say.

If you had a friend with a chip that is supported pre-update, i'd swap CPU's and flash the BIOS. But if that's not the case, hmmm....

Some MoBos support updating BIOS(UEFI) without CPU, you just need PSU.

If you don't mind microATX boards, the MSI B550M Pro-VDH Wifi seems to be a solid model based on reviews and it's on the budget side (close to $110 right now.)

It allows BIOS updates without a CPU via USB, in case it comes from the shop with an old BIOS version, and has HDMI, DisplayPort and VGA ports for the integrated graphics.

You could also get an A520 board if you want to keep it closer to $50, for example, but I don't know what limitations that chipset has. B450 boards work too with an updated BIOS.

About RAM, since the iGPU shares system RAM and this affects graphics performance quite a bit, you would want the fastest dual kit within your budget. 3600/16 kits are quite affordable and should be good enough though.

I have used Crucial Ballistix on my two Ryzen systems (Ryzen 5 3600 and Ryzen 3 2200G) and I haven't had any problems, but I was using an Asrock B450M Pro4.

Get an MSI B550 board with BIOS FlashBack. Personally I would avoid Asrock, Gigabyte or cheap Asus bords.

Why is MSI a good choice? Why are those other brands bad choices?

(Worth noting that my current desktop (the one that this computer would likely replace) has an Asrock motherboard.)

I have my eye for a while on Ryzen 5 5600G + Gigabyte B550M Aorus Pro-P combo. It has Q-Flash option if flashing the BIOS is necessary. Regarding the wraith stealth cooler on 5600G it is not loud but it is audible.

https://www.youtube.com/watch?v=ihg6XQiqW7A

This Summer i've built a PC for my parents Ryzen 3 4300GE + Gigabyte A520M DS3H for around ~$220 and it works great. Didn't even had to flash the BIOS, everything worked out of the box.

I've had bad experience with cheap MSI boards (B350 and a older FM2 socket board). Stuff like software bugs, slow updates and cheapo components that limit overclocking.

If you play games with it and like to use a controller, I would recommend a built-in bluetooth. The big antenna gives a way better connection than those USB-dongles. I get <2ms response with my DualShock 4.

MSI, Asus, Gigabyte... they are all good. Sure you can go into brand fanboy territory with all the little nitpicking if you like, but in general modern major labels are pretty good. All of them. Get one that is designed for gaming and avoid the dirt cheap ones designed for bitcoin mining and/or office work and you'll be fine.

I recently saw a review for a small package that could be interesting to you, the ASRock DESKMINI X300W.

https://www.youtube.com/watch?v=_raw4h7VfZQ

As others have said, you can on some motherboards update the UEFI/BIOS without a processor (I guess they have a microscopic processor worth pennies built in). According to Youtube channel Jayztwocents, this function works badly on ASUS boards even if htey may otherwise be fine.

Alternatively some factories update the UEFI/BIOS before shipping and slap a sticker on to tell you that.

Alternatively some shops have a service where they can update it for you. That costs €20 here, tax included so not expensive but this is Europe, not NA.

Please look for reviews or ask here before settling on a certain model as most manufacturers have had less well made models. Checking for the features you want is kind of your own task imho.

That's just my personal opinion, based on the research I did for my own system, and what I've seen on channels like GamersNexus and HardwareUnboxed, or Buildzoid/Actually Hardcore Overclocking, in the past 4 years or so.

Asus are good, but you have to pay a premium for their boards, and their cheaper ones are usually no better than the cheap ones from the other brands. Oh, and their software is blotware.

Gigabyte is a brand I find hard to trust, and the recent fiasco with the exploding PSUs just cemented my opinion about them. I remember Steve from GamersNexus saying a few years ago how, from his observations, Gigabyte motherboards usually feed a bit more power to the CPU on their auto settings. That results in more power consumption and higher temps, and that's a big no-no for me, as I'm not an expert to manually set voltages and whatnot.

Also, it seems that Gigabyte boards (Asrock too) use much looser auto timings for the memory. It's explained in this reddit thread.

I've probably seen and read most reviews for graphics cards (at least with AMD GPUs) on GamersNexus, HardwareUnboxed and TechPowerUp, and Gigabyte cards were consistently beaten by cards from Sapphire, PowerColor, MSI and Asus (and XFX in the last year or so - their RX 5700s were pretty bad). I'm talking here about their coolers, because performance is pretty much the same nowadays, regardless of brand.

Now Asrock, there's so much to say about them. Firstly, my experience with their B450M Steel Legend, which is not one of their cheaper ones. It's not a terrible board, but it's not that good either. I went with this one because at the time I was building my system, the motherboard I wanted to buy (MSI B450M Mortar) was nowhere to be found in my country. And I waited for about 2-3 months. Now I kinda regret the decision of going for an mATX system - the selection of good mATX motherboards is rather small.

I bought 3200 Mhz memory, but there's no way for it to go above 3000 Mhz, even with much looser timings. Yes, the memory modules are not on the Memory QVL for Matisse (Ryzen 3600), but nothing from that short list was available at the time of purchase. So here it is a small comparison for Memory QVL (Matisse) (mATX boards): Asrock B450M Steel Legend = 105 entries; MSI B450M Mortar Max = 2334 entries; MSI B450M BAZOOKA = 2230 entries; Asrock B550M Steel Legend = 133 entries; MSI MAG B550M MORTAR = 1723 entries; MSI MAG B550M BAZOOKA = 1716 entries. I guess these numbers speak for themselves.

BIOS updates with the AGESA Combo, usually, arrive much later for Asrock, but what's worse is that they removed some sensors readings from their BIOS, probably in an attempt to hide how bad the Power Reporting Deviation was on their boards. This happened to me, but also on other boards, as you can read here. So I reverted back to an older BIOS. I have yet to try the latest BIOS to see if the issue is still there. I also lost performance in newer versions, but I don't know if that's Asrock's fault or AMD's and their AGESA. In the time I've spent on Asrock forums, I've seen plenty of threads with problems for top-tier boards, like Taichi, not just for the cheap ones or mid-tier like mine.

Now, I'm not saying that MSI is the best brand. Every brand has good, mediocre and bad products. But from what I've seen/read, in the last few years, MSI seemed to be the most consistent with their quality, and most importantly, the only ones open to criticism, acknowledging their mistakes and actually fixing them. Some of their first models for the X570 (or it was B550??) were bad, but they fixed them afterwards. What did Asrock do after receiving negative reviews from HardwareUnboxed and GamersNexus? They blacklisted them - ha, like that will magically make the boards better. So, I guess, these are some of the reasons I trust MSI more than the others, at the moment.

My advice is not to buy the cheapest/lowest tier of any kind of product, and without reading some reviews from trusted sources. Here's a AM4 B450/X470 VRM tier list, but I'm sure there's one for the B550/X570 too, somewhere. If I were to build a system today, I'd just buy an MSI B550 Tomahawk or Torpedo and be done wit it.

I guess you got the answer right there. Cheap is cheap for a reason, regardless of brand.