RX 7900 (RDNA 3 flagships) are officially supported. I think the 6900 (RDNA 2) was supported at one point as well, and in both cases other cards with the same architecture could usually be made to work as well.
Looks like on Linux the only GPUs which are currently officially supported are the 7900 series.
https://rocm.docs.amd.com/projects/install-on-windows/en/lat...
On Windows the official support covers most (all?) of the discrete desktop 7000 and 6000 series.
[1]: https://rocm.docs.amd.com/projects/install-on-linux/en/docs-...
Seeing this, I am not surprised I misremembered the state of RDNA support in ROCm. The support matrix it pitiful compared to Nvidia’s CUDA support matrix.
Debian has a particularly good compatibility story. Its ROCm packages carry patches to work on all discrete Vega, RDNA 1, RDNA 2 and RDNA 3 GPUs. That's not official support, but it is tested.