Hey! Sorry it took me a while to answer. It was pretty hectic with new version and steam release on the way...
Anyways, for mac versions it's been a known issue that you cannot save if the game folder doesn't have the permissions from mac to create a save file. That could be the case, although I'm not 100% sure about your situation. If the problem in selecting a file, make sure your mouse is not hovering over the screen, because it can overlap with the keyboard commands
There should definitely be a possibility to just re-download the game from itchio if you bought it already. Don't go wasting more dollars into the game! D: If you can't find the download link or if the saving still doesn't work, send me email, I can work something out!