is there any workaround to sync 4 x 4UHD output from a MAC Studio Apple M1 Ultra ?
Thanks in Advance !
Short answer: no.
It is not possible to sync outputs from the Apple M1 Ultra's GPU.
You could use a Blackmagic Decklink 8K Pro inside a Thunderbolt chassis, but your would be limited to 4 x 2160p30 (not 4 x 2160p60 because of the Thunderbolt bandwidth). In this case, be sure to run the Decklink as a whole 4320p30 output to get frame-sync outputs (use video-routing in Millumin if needed.