I've tested this in Desktop mode and in Game mode on Steam Deck.
On first launching the game, mouse input behaves as expected in-game, with precise mouse movements resulting in precise camera rotations.
Losing focus on the game window, by alt-tabbing or launching another program in Gaming mode, causes the mouse movement to become "sticky": small movements in either direction do not cause any camera rotation, and large movements move the camera much less than expected. This makes the game uncomfortable to play.
On first launching the game, mouse input behaves as expected in-game, with precise mouse movements resulting in precise camera rotations.
Losing focus on the game window, by alt-tabbing or launching another program in Gaming mode, causes the mouse movement to become "sticky": small movements in either direction do not cause any camera rotation, and large movements move the camera much less than expected. This makes the game uncomfortable to play.