Similar problem. After upgrading my Macbook Pro (16-inch, 2019) to Monterey I started experiencing freezes and strange visual artifacts on some open windows... Can't exactly replicate, but it happens very frequently (so much so that is it is not feasible to use the second external monitor), and it seems to happen more when connecting the second external monitor. I have a Dell and an LG monitor. The issue happens with both monitors connected through USB-C - HDMI cables, connected directly or through a hub, when using the Macbook in clamshell mode. I have been successful in maintaining a stable setup running by making sure that the computer boots with the two monitor cables plugged in before hand. I also disabled the sleep option in the power configurations just to make sure, but I think the key is just to have the monitors plugged in on boot... Hope this helps. Also hoping to see an update/fix from Apple.

Similar problem. After upgrading to Monterey started experiencing freezes and strange visual artifacts on some open windows... Can't exactly replicate, but it happens very frequently (so much so that is it is not feasible to use the second external monitor), and it seems to happen more when connecting the second external monitor. I have a Dell and an LG monitor. Macbook Pro (16-inch, 2019). The issue happens with both monitors connected through USB-C - HDMI cables, connected directly or through a hub.