Give a screenshot of the whole gimp interface including layers and tool options such as this one
https://i.imgur.com/0Q67PyC.mp4
On the other hand it might be a MacOS thing. There is a tweaked version out if you use big sur as
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Updated on 2021-01-16: GIMP 2.10.22 DMG revision 2
Some performance improvements on Big Sur, possible regressions reported on older macOS (use Revision 1 instead if it's your case)
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https://i.imgur.com/0Q67PyC.mp4
On the other hand it might be a MacOS thing. There is a tweaked version out if you use big sur as
---------
Updated on 2021-01-16: GIMP 2.10.22 DMG revision 2
Some performance improvements on Big Sur, possible regressions reported on older macOS (use Revision 1 instead if it's your case)
---------