CPU
Some games benefit a lot from the large L3 cache in the X3D cpus, f.e. the AMD Ryzen 7 7800X3D. Check whether it is true for the ones you play.
GPU
I'm running an AMD 6650XT GPU in Linux without any trouble, I even use vfio to use it in a Fedora VM without errors.
RAM
Buying 2x32GB gives you enough RAM to run a bunch of VMs while gaming. 2x16GB is more than enough for a gaming rig.

Your friend is right -- AMD graphics on Windows can be a pain (last I checked)

That said the reverse is true on Linux, AMD GPU is fucking sweetas -- I got at least a dozen or 2 dozen AMD GPUs > 2016 and they kick ass, never gonna give them up or let them down :P

There's a reason AMD is crushing it on Linux

AMD Ryzen 7000 vs 9000 isn't a huge difference iirc, mostly more efficient. The X3D variants are definitely worth it for gaming performance though, so I'd wait for the 9000 X3D reviews to compare.

32GBs is plenty of RAM for now, 64GB is overkill for gaming purposes. I don't use 100% of my RAM ever and that's with Discord and a bunch of browser tabs open while playing Cyberpunk or heavily modded Minecraft.

For the GPU, I currently use a 7900 XTX and haven't had issues running that with Manjaro Linux. Haven't used an Nvidia GPU with Linux, but from what I can tell their support was/is dubious but improving.

I had similar worries about the AMD driver stability before I switched from NV about 5 years ago. But my experience has been great even back then and things have only improved since.

One data point to consider is that Valve is shipping the Steam Deck with an AMD AMU and stability and compatibility is paramount for that use case.

Nvidia GPUs seem pretty solid with the latest driver developments around Wayland explicit sync now. I haven't had the experience with a modern AMD GPU to compare, so hopefully others can chime in there. I think AMD stability depends on which driver you use.

As for AMD CPUs, I don't think you can really go wrong if you go with the x6xx class or above. The X3D variants are supposed to have a bit of an edge in games but a very slight penalty in other general computing tasks. Doubtful it would be anything perceptible other than in benchmarks or compile times. If your system is primarily being built for gaming, I'd say opt for an X3D part if all other things are equal. If it's more of a workstation kind of system, or you plan to leverage a lot of virtualization tech, I'd say spend as much as you're willing to stuff as many CPU cores into that machine as you can.

As for memory, more is always better. I've got 32 GB on my main system and never felt like there was anything it couldn't handle, and that's even being somewhat sloppy leaving other fairly memory intensive programs running in the background while I game. In that department, I'd just go with 32 gigs and call it a day, unless you're doing video capture/editing.

Nvidia Gsync shouldn't be an issue in Linux, at least not with an Nvidia card. If the monitor doesn't also support Freesync, then that might cause a hassle with an AMD card.

Good luck and have fun!

Mine is a few years old now (so not the absolute latest and greatest, not that it was to start with lol) but when I built it, my spouse also built his at the same time. We have very similar builds with some minor differences. But the two biggest differences are the GPU (mine's an AMD Radeon RX 6800 XT and his is a Nvidia with almost the same stats) and the mobos. My experience has been completely problem free. Everything has just worked. His GPU has been giving him problems up until more recently. Even then when something goes flaky he has to work out if it's because it's a Nvidia. He regrets not getting an AMD. His mobo is also a bit weird with Linux but only around the rgb lighting. It's a Gigabyte whereas mine is an ASUS. So if you get a Gigabyte mobo, I would just double check compatibility if you care about RGB lighting.

Is there anything i should steer clear of mainboard wise? MSI/TUF gaming? Anything that is overpriced and not necessarily better quality?

I had lots of trouble with my GTX 1080 on Linux back in the day, but my understanding is that newer cards are slightly better supported. I got a 7700XT a year or so ago and it’s been super stable for me.

AMD graphics drivers on Linux are open source and community supported. On Nvidia is almost a requirement to use their proprietary drivers which get very little corporate support for gaming/desktop usage

I have Radeon 6900 rx and it games sweet on Linux. I've played games on Windows with it too without issue (dual boot).

Generally, AMD is king on Linux, Nvidia is suffering (had drivers updates break OS installs). Nvidia is only really if you want ray tracing or Cuda, and I've never needed to.

OpenSuse Tumbleweed is my distro of choice. Up to date kernel. Rolling distro. Stable.

Curious too, im still running an FX-8350 with a 1060. It is fine for what I do for now but I think I've gotten my money's worth.