I stumbled across a solution for what seem to be AMD GPU hangs on Zen 4 and Zen 5 laptops. If I roll the amdgpu linux firmware files back to those from 202503, the hangs on both systems don’t occur at all. I am not sure how/where to report this - I assume AMD screwed something up.
The symptoms I was seeing would be a black screen with fixed cursor after waking the screen, or a wallpaper + cursor (which won’t move) after logging in to Plasma. There was no way to switch to another terminal on the host, but one could SSH in and interact with the system. It seemed to be fairly random - not every wake screen from sleep would wedge. Sometimes it would coincide with disconnecting the power supply, but not every time.
Since rolling back the firmware and holding the package, I have yet to see a single hang like this.