Depends what support means to you really. The docs use support to mean things AMD tested and expect to work, modulo errata.
If you're building the stack from source or found it in a Linux repo, decent odds it'll work for you. More likely to work on gfx9 or gfx10 than the older cards. I think that's roughly the last five years.
If you use the official distribution, some parts are compiled to gpu-specific machine code and if your gpu isn't one of those, you can't use that library. I think there's a reluctance to compile the libs for GPUs that aren't in the internal CI in case they don't work.
As an anecdote, I do most development on unsupported hardware, unsupported distro and unsupported kernel, with the upstream driver, using whatever was on llvm main that morning. That mostly works despite positioning myself as most likely to run into bugs.
