I was under the illusion of being the only alone having difficulties to ever understand the tools on GIMP.

That tool really needs a makeover in terms of usability. It has been at least 20 years and I still don't know how to use beyond the basic there.

Please don't recommend android distributions with a shady funding model and that force users to buy expensive compromised Google hardware.

There are good options like LineageOS and e/OS/ that run on a huge variety of android devices without suspicious limitations.