After extensive testing, we have found that Maid Mansion runs best while in the Steam Deck's Desktop mode. If you're unfamiliar with how to get to it, like how I originally was until very recently, use the following steps:

Steam Deck to Desktop Version
1) Press the STEAM button on left side of your console's front side.
2) Select 'Power.'
3) Select 'Switch to Desktop.'
4) Steam Deck will now switch to the Desktop version.
5) Select Maid Mansion from the Desktop and Launch.
6) If Maid Mansion is NOT visible on the desktop, click on Steam Deck logo in bottom left of taskbar.
7) Go to 'Games' and search for Maid Mansion.

Once Game has Launched
1) Check Settings from Main Menu
2) Make sure game is in "Full Screen" mode under Display

When Finished
1) Quit Game
2) Select "Return to Gaming Mode" from Desktop to switch back to normal gaming mode on the Steam Deck.

If you have questions or concerns regarding Maid Mansion on the STEAM DECK, please share them with us here.