Pixelmator Pro does work on the beta version of macOS Sonoma. However, as with any beta, there's a chance that things won't be working as expected. Don't use the beta to work on important files or, if you ignore this advice, make sure to back up any documents before you do.
I've had zero errors with Pixelmator 3.3.8 and Sonoma 14.0 (23A5276g). In fact, for what it's worth the only error I've had with Sonoma Public Beta thus far is complete lock up playing any videos in QuickTime Player.