Thank you!
Yes, almost working I think. z80-embedded is now an accepted combination on the Cross tab, and Install Compiler indicates "That went well!"
However installation of z80-embedded deletes the ppcz80 executable file from fpc/bin/aarch64-darwin.
(if I re-install z80-zxspectrum afterwards, ppcz80 reappears).
I have managed to clone and build fpcupdeluxe 2.4.0jp successfully too, so I can probably test any further changes quite quickly.