Selection not showing on Mac OS Big Sur 11 though "Show Selection" is enabled
Edit on 2021-10-16: we have now confirmed the fix for Wayland (#5640 (closed)) also fixes the issue on macOS BigSur. This fix is currently only on our main development branch, which means you will get marching ants
For the record, it means the reason is probably the same as explained here which is that macOS must have changed the way it draws windows since BigSur so some things we used to do to draw our windows on the screen are simply not possible anymore. It also means even old versions of GIMP would be affected (as confirmed by this message which even tried a 2.8.x version) since the change didn't happen in GIMP but in macOS.
Edit on 2021-06-25: it might have been fixed on the master branch (cf. #5640 (closed) with similar symptoms on Wayland/Linux, hence possibly the same causes). But as long as none has built GIMP master for macOS, we won't be able to confirm the fix. If confirmed, we may try to see how this can be backported to the 2.10 series.
After the last update on my MacBookPro, Gimp now won't show what is selected. All selection tools are the same. They allow a selection to be made, but once you release the mouse button, the dotted line showing the area vanishes. The selection is still there, but you can't see the edges of it.
I tried uninstalling and reinstalling the latest version and it's still happening.
Message to any other person who has this issue: if you don't have any information you think may be of interest to understand and fix the bug, or even better code to contribute, don't leave a message, please. Thanks!