In my experience, this is a new issue arising with InDesign 2023. Anytime the cursor is active in a text frame, the pasteboard flashes in sync with the cursor. If I click another application so the cursor stops flashing, the pasteboard also stops flashing. If I select the frame or something else in InDesign so the cursor disappears, it stops flashing. But anytime the cursor is active and flashing, the pasteboard also flashes. It's very annoying and distracting, and assuming it's a graphics issue, I deactivated GPU Performance. This fixed the issue. I'm on iOS 11.6.7 (with Apple M1 chip obviously). Video attached to demonstrate.