Go AMD. The open-source drivers already provide the best performance compared to the closed-source ones, and are included in the kernel and Mesa, which means the cards will work out of the box. For the best performance and latest drivers and optimizations you should switch to a distro with more up to date packages than Debian if you plan on buying a current gen card tho. For example, Fedora is a very good mix between working OOTB, ease of use and bleeding-edge packages.
nVidia is… difficult. The open-source drivers are getting better but are still way behind closed-source drivers, and each closed-source drivers version only works with a single kernel version. It might work OK as long as the drivers and kernel are kept in sync (I think Pop! or Nobara have nVidia specific versions for this reason), but otherwise each kernel upgrade is a risk. Plus nVidia drivers are basically shit with Wayland and cause a ton of issues.
Intel has a good track record with iGPUs so discrete cards should be as trivial to use as AMD ones, if more at the entry-level performance-wise.