"Real-time patched Linux kernel for low-latency desktop use" - does this really make sense? I think there have been various efforts like this over the decades but as far as I remember none of them really made a huge difference for the end user.

IIRC the realtime patchset that RHEL maintained in its own branch/tree was upstreamed last year.

I don't think it makes sense for desktop applications, it may make sense if sound latency is a priority but even then stock kernel delivered lower latency in many cases.