The issue is one of licensing, not technology. There's all kinds of patents in the space, and using free codecs could still infringe them. DirectX doesn't have the same patent protection. I believe in theory you could make a fully open source Linux native version of DirectX.

For more info from someone who knows more than me, see here.

Well, sometimes Windows games depend on propietary codecs, and until Valve can get the devs to make adjustments so the codecs aren't needed, the games aren't going to work properly in regular Proton.

If GE received a Cease and Desist, that would be frustrating, but linux gaming would go on. If Proton got a Cease and Desist, that could be catastrophic to linux gaming. Valve could even theoretically get banned from working on linux gaming (like the Yuzu devs got banned from working on emulation). It's just not worth the risk for compatibility/performance for a smaller proportion of games.

I need some advice on what to throw on this laptop - and some suggestions on how to squeeze the best performance out of this (Optimus vs. Proprietary NVIDIA vs. Open source drivers).

One thing here, the open source Nvidia drivers still have a lot of performance issues. It's only fairly recently that NVIDIA has opened their drivers up enough to allow any kind of reasonable performance from open source drivers, and getting them up to par is still a work in progress. So stick with the propietary drivers for now, but keep an eye on the new open source driver, NVK.

(As far as distro recs go, I recently started using OpenSUSE Tumbleweed and am really liking it, but I don't have enough experience with it yet to make an informed recommendation)

Nvidia already opened their driver, at least to the same extent as AMD, which is why NVK is able to exist.

I’m not sure about the latter

I believe it was Xwayland 24.1 that recently released that brought explicit sync support, so you'll need that.

Seems like a good redesign.

Yep, this is what I had to do.

Nvidia users will also need a DE update, but yeah, we're finally almost there.

will not solve issues with compositors not having it

Many compositors already have patches for explicit sync which should get merged fairly quickly.

graphical libraries not having it

Both Vulkan and OpenGL have support for explicit sync

apps not supporting it

Apps don't need to support it, they just need to use Vulkan and OpenGL, and they will handle it.

Wayland doesn't implement sync of any kind, they probably meant to say "the Wayland stack"

Wayland has a protocol specifically for explicit sync, it's as much a part of Wayland as pretty much anything else that's part of Wayland.

Nvidia is not the only driver that needs to implement explicit sync.

Mesa has already merged explicit sync support.

YouTube Music. Google Music doesn't exist anymore.

You might find just the inbuilt linux (crostini) under chromeos is fine..

Crostini is only sort of built-in Linux. It's more like a built-in Linux VM, and performance suffers a bit because of it. If they're not doing anything heavy, you should be correct, it'll be fine.