Emulator Issues #12450
OpenGL SSAA not working with Radeon GPUs
The sample qualifier appears to not be working properly when used inside an interface block and seems to affect all Radeon products. This driver bug makes SSAA look like MSAA when used. Disabling the usage of interface blocks for Radeons when SSAA is enabled should do the trick, or just always disable it like in DuckStation.
I confirmed it happening with 5.0-13827, no new changes since. So I'll assume it's been happening since SSAA has been available when using interface blocks. The template seems tailored to game bugs in particular, so I just deleted the thing.
I haven't tested linux, so it's a Windows only driver bug as far as I know.
PS: OpenGL Anisotropic is also broken on Windows with Radeon cards, old cards are safe though. No workaround that I know of.