Thank you, I'm glad you enjoyed it :)
I don't have an exact estimate about the hours in the game rn, but its a few hours at the moment.
In terms of your issue, my only recommendation would be try moving the download to your Applications folder? It could help, please let me know if it doesnt and I'll do some more research!
Update - not that I have any expectation of you, but thought you might be curious - seems to be an issue with the itch desktop client! Or possibly MacOS security? idk
Can't save games that I've installed via the client, but if I download and manually install (and override system security for each game to allow me to actually launch them) I can save... interesting... and bothersome, but hey, love a successful workaround.
Oh and it seems RenPy may indeed also be involved, as I have MDRG installed thru the client and it saves fine.