Currently when generating a library for .proto-files you have to manually specify the libraries to link with in a separate cmake-call.
This issue tracks adding support for it to be automatically picked up or adding LIBRARY/PUBLIC_LIBRARY arguments to the qt6_protobuf_generate cmake function.
The solution it ends up on should be most appropriate (doesn't feel like too much magic) and reliable (it should always work or let you know what to fix if it didn't)