I see what you are saying. Re-installing Gimp rarely does anything. Often it is some user setting that is no longer obvious and these settings are held in your Gimp profile which remains between installations.
Try Edit -> Preferences -> Tool Options and click on "Reset Saved Tool Options to Default Values" Restart Gimp, see if it makes any difference.
Otherwise a clear screenshot of the whole Gimp interface with open image, tool options, layers, any open dialogue might help, someone might spot an overlooked option.
Try Edit -> Preferences -> Tool Options and click on "Reset Saved Tool Options to Default Values" Restart Gimp, see if it makes any difference.
Otherwise a clear screenshot of the whole Gimp interface with open image, tool options, layers, any open dialogue might help, someone might spot an overlooked option.