I posted this bug report in 2022 but it remains a bug even today, 18 months later. Someone responded to tell me that in Windows, the same issue does not manifest.
The problem is that when you invoke Check SPelling, the window in which corrections are shown and performed is in a fixed position that cannot be moved like a modal window. As a result, many of the incorrect words that are highlighted and covered up by the window that cannot be moved away to see what's underneath it.
