I did do one thing that I thought was creative, but is really only useful in my use case. For the libcamera integration, indi-allsky thinks it is talking to a normal indiserver.
indi-allsky uses the pyindi-client to interact with INDI. Therefore, I had to write a fake pyindi-client class to emulate the behavior of this module. indi-allsky still calls functions like connectServer(), but they do not do anything.
I installed Bullseye 64-bit, used the build_indi script and connected the HQ camera via libcamera (I installed on raspy 4, that's much faster compared to raspi3). This seems to work on raspy 3 & 4 , both services are now running.
I now want to get some experience and might com back with questions if needed.