I have this issue with Glyphs 4 on a mac mini with an M4 processor: holding the Option key and moving the cursor causes a visual glitch where glyphs zoom in and overlap.
This didn’t happen to me in Glyphs 3.
Here is an example before and after holding the Option key.
EDIT: I’ve discovered that it isn’t visible at exactly 261 pt preview size and for bigger values it is zooming out to 261 pt.