this seems like a bit of an oversight to me.
There’s a driver bug introduced somewhere between kernel 5.18.12-3 and 5.18.16-1(it deals with memory clocks/gpu power management, so I’m assuming it’s kernel AMDGPU driver), that causes GPU memory clocks to be locked to a low level at certain refresh rates(99~144), and seems to also have caused some stutter at higher framerates/gpu loads even with memory clocked up,
But, I can’t report it because of the forum rules.
Of course, it’s probably not even manjaro related, but kernel org bug reporting also doesn’t want bug reports outside of kernel developers, and their terms are to report only to distro bug reports for distro use.
You need to compile vanilla kernel though, and test that. (if that works, then it probably is Manjaro’s fault)
Also:
You possibly need to pinpoint which commit is causing the issue (by bisecting), and you are giving a kernel range. If you can’t pinpoint even a single kernel that’s supposedly causing an issue, I wouldn’t be surprised if it’s not kernel’s fault at all.
And last thing; 5.18 is getting EOL soon, so no one will fix anything anyway, probably. Time to move to 5.19 or LTS.