Solved - TWP in Steam no longer installed - Not exactly right here but

[Sushi]

on the getting more saveslots, you can try it in this way:

Recovering an old auto-save file

@ema it really is quite simple: the autosave slot is called Savegame1, the others are named Savegame2,… up to Savegame9 the savegame consists of the .save file and a .png for the thumbnail So copy/rename any manually saved game and its thumbnail to Savegame1 to put it back in the autosave slot Or vice versa copy the Savegame1.* files to another one to make a manual save in another slot Note that you can use the same technique to copy additional save-points in the game without being limited …

and

Using Windows Store save games with Steam

@ZakPhoenixMcKracken, this is not where the same games are stored on Steam. They are in AppData\Roaming\Terrible Toybox\Thimbleweed Park

So if you backup your savegames per playthrough or any other way you’d like to organise them - by act, by flashback /start/end/… in separate folders, it should be pretty simple to find back exactly what you want in even 10 years.