Just giving a quick update on this, I deleted the compatdata for this game and the tearing was mostly eliminated.
If anyone needs to do this themselves, please back up the compatdata first, as it contains the game's save files (there's no Steam Cloud support).
Nothing extracted yet.
Compatibility Report
System Information
I confirm:
steam-2017080.log
Symptoms
Reproduction
I should note at first the tearing wasn't very noticeable, until I had connected the Deck to an external monitor. At that point the tearing was worse, even after disconnecting from the monitor.