Y’know what worked? Newbies to Linux are going to hate this answer, and I admit that it is going to get a little “I use Arch, BTW…,” because that’s exactly what worked, and I fully believe that if you’re going to install Arch, you should:

• Be fully ready to embrace wiki.archlinux.org as your new bible, and do more reading on forums than posting questions. That doesn’t mean questions aren’t welcome, it means you need to determine that the question isn’t answered in a way that addresses your issue, before asking it (again). In short, installing Arch is not for the faint of heart, and is rarely for newbies; I mean no disrespect by that, I mean you need to be serious about what you’re doing, and not expecting anyone to come to your rescue. There is no multibillion-dollar, international company interested in coming to your aid so they can keep the nozzle of your personal data flowing to them, and fellow Linux users, you may have noticed, while very helpful in some situations, can (as we all can) be kinda crabby sometimes… particularly when they think you haven’t answered a question through before asking it (and sometimes just piling on from there).
• All of the above said, it is OK to use the archinstall command, as long as you are sure to have handy the resources mentioned above.

I simply will not walk you through the steps to install Arch, because you need to learn it for yourself; you need to get yourself into trouble and figure out how to get yourself out. It’s a necessary part of installing any operating system that was not packaged for “gaming.” Is it the first step I would recommend anyone take away from Windows? No. But after you use Linux for a while, it might be a good step to take, because you can teach yourself so much more by experimentation.

Why did I settle on Arch? The short answer is, regardless, twofold: it’s what I was happily using for years before CachyOS came along (various Ubuntu derivatives before that), and because it’s what CachyOS is based on (the CachyOS team develop their packages off of the Arch base). The long answer is that given the first part of the above, I knew from experience what would work for me, and what wouldn’t; what I’d tried & not gotten to work, and what tooling and muscle memory I had settled on over the years of using Arch (and later CachyOS).

That tooling and muscle memory is not what we are all told works best for gaming performance, but after extensive testing for my hardware, it’s what has always worked for me, including with the best performance (yes, I would install KDE Plasma, boot up into it, and experience lower frame rates than the same system booting into GNOME, which is the DE I prefer. On my system, with a heavy pinch of “YMMV,” that is not confirmation bias, it is what I have run the benchmarks to have the data, to prove to myself. And yes, I’ve proven it to myself and not to you, because I didn’t build a gaming rig for you.

Anyway, so after I reinstalled Arch and ran it vanilla, of course gaming performance was somewhere between <1% and <10% worse by FPS, depending on the title. This was expected, and I had decided it was fine because in terms of other daily driver use, I really needed protonmail-bridge to work with Thunderbird, and whatever script archinstall had followed to install GNOME, it did in fact just work, where whatever CachyOS is doing these days to have Calamares install GNOME, is not allowing protonmail-bridge to work; this is my original concern as in my post above.

My suspicion (as in the previous post) is that CachyOS is following the trend of supporting the general idea of KDE Plasma being called the DE to offer better gaming performance, and therefore to no longer support automatically installing several common GNOME packages in their Calamares script. I don’t know which ones & I don’t know fully why, other than likely being told that they are concerned about potential conflicts with their KDE Plasma/Qt (as opposed to GNOME/GTK) counterparts.

Aaaaanyway, so I was fine with the OK but not utterly amazing gaming performance in Arch, and with the other parts of my daily driven use of the rig, working how it should. I tinkered with installing proton-cachyos-slr from the AUR, and it improved gaming performance over proton-experimental a bit (~<1%), but not dramatically.

So I got to thinking, with my system configured fully how I want it under Arch (as opposed to how Calamares configures it when installing CachyOS, and my having to hunt around for what packages and configurations make it work more like what I want… and famously for protonmail-bridge, never getting there), there is a way to use CachyOS repositories and packages on an existing Arch install. It is discussed by the CachyOS team at this link: Optimized Repositories | CachyOS

I ran the automated script as listed. That updated all of my system’s packages that had newer CachyOS versions, to those new, architecture-specific (whether Intel V3 or V4, or AMD Zen 4/5) optimized packages. That helps a lot, but I wasn’t done yet. I installed cachyos-kernel-manager, and installed the cachyos-v(#) kernel appropriate to my architecture. Note that that doesn’t make the computer start up with that kernel, or even make it an option upon startup. Also note that I can only tell you how to manage that, if you have installed Arch without UKI enabled (because I had little enough experience with that, to not select it when I used archinstall to install Arch).

If you are not using UKI, you should be able to simply go to /boot/loader/entries, copy whatever entries are there into “-cachyos.conf” versions, and rename the booter entries, then point toward the correct cachyos “vmlinuz” and “initramfs” entries on the same root volume, with the same options (or boot parameters). I know there’s a way to do all of that for UKI; I do not know what it is, and if you choose to add CachyOS kernels, you’ll have to do your own UKI configuration research.

Once I had done that & successfully booted to a CachyOS kernel, I also had to remember to install cachyos-settings, so that the game-performance command would be available to your Steam games’ launch options (where you might have put gamemoderun before. That reminds me; I can probably uninstall the gamemode package.

So how’s it running? Performance is back up to CachyOS standards, and on some titles, it seems to be ~<1% greater than those! Of course, I can’t be absolutely sure of that because packages have been updating all throughout this process, across both Arch’s and CachyOS’s repositories. But it seems a bit faster, and if it is (which I admit in this particular estimation, if not the one mentioned further above, may be confirmation bias), it may be because I haven’t installed all of the other bells and whistles Calamares does to CachyOS, to appeal (maybe?) to newbies; I’m talking about their recent move from Octopi to Shelly, etc.

I have it running what I want, not running what I don’t, and I’m happy (at least, for the moment) with it. It is, at its base, Arch, with CachyOS refinements. And it lacks what I consider to be (and you may not, and that’s fine) the cruft of CachyOS. Oh, and protonmail-bridge continues to work with Thunderbird, which is all I had wanted in the first place.

So my way to resolve that problem is a lot for a newbie to either Linux in general, or even to Arch in particular, to take on for themselves. Just be warned, and if you’re still interested, be ready to read and learn a lot. Good luck!