've seen this error message, but I don't understand what it means because the emulator doesn't seem to be in software mode. It might be related to RetroArch. If you have enabled the Vulkan driver in your setup, you can get rid of this error by using the Vulkan driver in RetroArch for this core

[ERROR] Requesting OpenGL context, but RetroArch is compiled against OpenGLES. Cannot use HW context. [ERROR] [Environ]: SET_HW_RENDER - Dynamic request HW context failed. [ERROR] [Environ]: SET_MESSAGE_EXT: Unable to find or open hardware renderer for frontend preferred hardware context. Falling back to software renderer.

Quick update. For unrelated reasons I had to rebuild by system. I tried this again, renaming files and M3U entries .CD1-2 etc. Everything now works as expected.

I was totally convinced this was user error on my part. Apparently not. Queries resolved. Thanks all.

@badfurday they are not Zipped.