Using amdgpu on that card has been considered experimental ever since it was added like 6 years ago
If I recall right, it hasn't been enabled by default simply because it is missing some features like analog TV out support (which most people don't want or need in 2024).
There's many 16gb AMD cards since at least the 6000 series. The 7600 XT is probably want you're thinking of since the 7600 is only 8gb.