The problem, I believe, is that stable diffusion presently only supports Python 3.10, but Arch ships 3.12, and some of the dependencies aren’t compatible with the newer version. Here’s what I did to get it working on Arch + AMD 7800XT GPU.
Install python310 package from AUR
Manually create the virtualenv for stable diffusion with python3.10 -m venv venv (in stable diffusion root directory)
This should be enough for the dependencies to install correctly. To get GPU acceleration to work, I also had to add this environment variable: HSA_OVERRIDE_GFX_VERSION=11.0.0 (Not sure if this is needed or if the value is same for 7900 XTX)