By default, gpu info should show on btop but dependencies are not installed (on AMD GPUs. Not sure if it affects GPUs).
Unfortunately the dependency can only built with git clone or AUR. I suggest using AUR.
Here's btop's documentation on GPU monitoring:
https://github.com/aristocratos/btop/blob/main/README.md#prerequisites
Dependency links :
https://archlinux.org/packages/extra/x86_64/rocm-smi-lib/
https://gitlab.archlinux.org/archlinux/packaging/packages/rocm-smi-lib
GPU monitoring then shows correctly on btop.
(I posted this in case someone had the same issue/need)