Hello Xenosous, Panic recently changed the way that side loading via the website works. It means that v1.1 will have been installed for you in a different folder than v1.0 and that you'll need to plug you Playdate into a computer to copy the save files across.
You probably also need to save a game in the new version first, such that the game's save folder gets created (e.g. if your main game is on slot 1, then start a game on slot 3).
I'll try and post some more detailed instructions later on.