No way to stop scan once start it, it would be better if there is a stop button.
Until this is implemented, you can safely abort BleachBit by clicking the "X" to close the application window.
Fixed in Git commit 60eb46d333397daa720e2ed4e20b6b247255ee35
If you are on Windows, you can test CI build 2.3.1135 or later from https://ci.bleachbit.org
You could test the fix in the newly-released BleachBit 2.3 beta