The Free Software Foundation Europe (FSFE) has now put the important topic of Android aftermarket firmware at the top of its agenda in November 2021 as part of its Upcycling Android initiative.
The procedure of flashing an Android device with alternative firmware is not exactly trivial, which is why I have been offering this service to my customers for some time now. Please read more about this here: https://www.webdesign-markward.de/android-custom-rom-installation.html
I am also active for all Oldenburg residents within the framework of the Resource Centre Oldenburg.