Great first jam game!! Hope to see more from y'all in the future. The aesthetics are wild and the music is perfectly tense and frantic. And I love the godlike king rats at the peak! I was a bit confused about the warning sounds, but I couldn't look around easily which might have been a part of it. I think the big issue is that the mouse wasn't being captured.
In Unity I think you should be able to fix that by including something like
Cursor.lockState = CursorLockMode.Locked
which locks the cursor to the center of the game view and hides it, after Enter is pressed to start the game. Then you can set it to CursorLockMode.None after the game ends so the player can click around again in the menus.
Currently it does work better in fullscreen, but full screen isn't a total fix, especially for users who have multiple monitors! If you have another monitor, you can move the cursor right out of the game window which can make it easy to accidentally click out of the game entirely.