Might I ask which:
- Which Thinkpad? (CPU model and graphics would be helpful)
- What resolution and refresh rate of monitor?
- What does the trackpoint do during this? I know you said it's not the mouse, but I'm just curious.
If it's a modern-ish Thinkpad (like ~2018 or newer), these problems are weird and I have no advice to offer, but if you're one of those guys who daily-drives a Core 2 Duo Thinkpad, I'm curious how they do when hooked to a 4K monitor.