Dungeon Siege 1 on the Deck

I‘m trying to play Dungeon Siege 1 on the Deck. According to ProtonDB - with some adjustments - it should work just fine.

However, when I‘m trying to install the game, the „Install“ button is greyed out and it says „Available On Windows“ next to it. If I tap/click the install button, nothing happens. So the game doesn‘t even download.

I haven’t encountered this with any other game. I think I had the game installed on the Deck before, it already has launch parameters (just res and such) configured for the game. Either something changed or I‘m doing something very wrong and I‘m trying to figure out which it is.

Since the Deck doesn‘t give me an error message and googling the issue didn‘t return anything useful either, I have nothing to go by and I‘m hoping someone here can give me a pointer. Thanks!

Edit: u/CannonGoBoom‘s solution solved it!