I have now deployed using fly deploy --no-cache --local-only
(before that I did update Docker for Mac) and the deploy ran way slower (network I guess) but the deploy was successful and interestingly: the binary now runs on the fly server without “Illegal Instruction”.
Not sure what it means though. I would have expected the local build to cause even more issues (that’s why I did not try it before) because I expected that my M2 Mac is a different architecture to the one on fly.
That said: there are so many moving parts involved that I’m not certain whether me using --local-only flag fixed it or something else.