That’s a weird one! I’ve tried to reproduce it using my iPad Pro (4th gen) with Magic Keyboard. Like in your video, I used the touchscreen for a while, then selected stories with the trackpad (and switching back and forth between the two input methods).
Unfortunately, I wasn’t able to reproduce the issue, and can’t think of any reason why it would occur, other than at the OS or hardware level. It does kinda look like a hardware issue, since the pointer disappears in your video. The app doesn’t distinguish between touches on the screen or with the trackpad.
If you can refine a sequence that reliably reproduces the issue, let me know and I’ll try that. And I’ll keep an eye out for it happening.
Can anyone else reproduce this issue?