I would not be surprised if we found out that his ankle injury in the playoffs lead him to sign the Supermax Extension.
Plus, if he really wants out of MIL, it seems to me the his best option (in terms of financial benefits, practical implementation, and optics) would be to sign the Supermax Extension, play the required year, see how it goes, and if it continues to suck, demand a trade as wanting to play for a winner.
Waiting a year to sign the Supermax and then figuring out how to bail on MIL seems sub-optimal to me.
Unless somehow MIL has some unexpected success on the basketball court, I doubt Giannis will be playing for MIL in five years.