Yes, I and others have Zynthian running on CM4 with at least 2 different carrier boards - CM4IOBRD and Seeed Studio reTerminal. I don’t anticipate any major problems with CM5, it’s supposed to be compatible with RPi5. Of course there could be a glitch or two, but I’ll be surprised if there is. OTOH it wouldn’t be the first time I’ve been surprised.
Edit: There was some discussion about this a while ago in Compute Modules and the next Zynthian
It left off with “we’ll have to talk about this when the CM5 is actually available”.