My bad, I actually had the "production" trace command set to look for `XGetSelectionOwner`, but mis-pasted into my comment ;) Will that fare any better? It did make a few more PIDs/culprits end up in the trace output for me after all.

You are correct that "bringing your own function"/shared object will break that particular bpftrace script, but I would assume one could find a way to set up a probe in the X server, where all clients messing with clipboard state via some kind of IPC have to pass thru? (Again, I can only wildly speculate how X11 works under the hood - kinda shameful that I never bothered to look over all these years :-S )