This is a bit of a weird one but I wonder if anyone here has any ideas: when using Quick Sync for encoding (iGPU) I am unable to use ICQ rate control and am only able to use the QP metric (but at least it's still QSV). Activity log shows ICQ is absent from identified hardware capabilities. Been using the Handbrake container for a few months and apart from this I haven't noticed (or at least can't recall) any other issues.
However, recently I decided to experiment with a Windows 11 VM - iGPU passed through with the help of the Intel SR-IOV plugin - and when using Handbrake inside ICQ shows up with no obvious problems. Encodes seem to work; speeds seem unexpectedly fast but unsure if that's indicative of an issue or more so the file I chose to test with, will have to try some others.