SE‐0236 states:
A package will be assumed to support all platforms using a predefined minimum deployment version. This predefined deployment version will be the oldest deployment target version supported by the installed SDK for a given platform.
I understand that to mean that when nothing is specified, each toolchain will default to as old as it is capable of. Is this the case or not? If so...
It looks like nanopb is just restating the defaults in a forward‐incompatible way. nanopb could make the problem go away right now by removing the explicit deployment targets.
That wouldn’t solve the general issue with SwiftPM, but it would mean you wouldn’t have to wait for another toolchain to be released to fix your particular case.