I’m way out if my depth here, but isn’t certain things faster to render on the CPU still? I believe it is mostly vector graphics - I have seen a few papers showing that it can be done fast(er?) on the GPU but that may not be that widespread yet.
It really depends on the context.
If you look at it in a certain light, fonts are just "vector graphics" and there are ways to do that without using SDF (signed distance fields) and get really high quality precisely positioned fonts fully rendered on the GPU.
An example of that is the GLyphy project and we have a branch which can render fonts using that with GTK 4. It's a bit slower, but better quality and still easily able to handle 144hz full screen text scrolling. It requires some preprocessing before uploading glyph curves to a data atlas on the GPU.
For other shapes, there are options, but given GTK has so few upstream developers, they aren't quite ready for prime-time so they'll likely be part of GTK 5 in the form of "GskPath" if you feel like browsing the branches with that.
Indeed correct unicode text rendering is one of the difficult problems. It's the same thing that is missing from basically all games. So when people say stuff like games can run at 120fps, how hard can UI be? it's basically the same Windows 95 argument. The UI work being done is a small subset.