Hey hey. Really sorry to hear that you're having that problem with the Mac version. If you have a look at the most recent comment on the thread about getting the game to open on Mac, it seems as though that person is having the same issue. I responded to them a little earlier with something to try, but I don't think it's going to work. Still, feel free to read through my reply there to the person with the username 'Catherine' because I've gone into more detail there.
Since both of you have managed to get the game to launch, it seems to be a problem with Naninovel rather than with Unity. Likely a Nani initialisation issue. I browsed the Nani support channel on Discord to see if any other devs have encountered this problem with Mac builds. I found a few people mentioning it. One was back in 2020, and another was in February this year. However, I could not see any solution posted >.< I have sent a private message to one of the devs who was asking about the issue and how to fix it to see if I can try and find out from them if they ever managed to fix the problem for their game. I have no idea if they will reply to me or not though.
I can also try asking in support myself to see if I get a response from the software dev or any other users who may have run into the issue.
I wish I had a Mac myself so that I could test stuff easier, but without one, it makes it really hard to try and fix any issues that arise with Mac. I don't understand why on earth Macs are so dodgy for getting stuff to run on them >.< It seems like any Mac build I make on Unity only has a 50/50 chance of working.
What version of MacOS are you using? Catherine said they're using Mojave 10.14.6. I just thought I'd ask because if I post in support, the software dev might need to know in order to try and help figure out what the problem is.
Anyways, if it looks like it's not going to be possible to fix, please don't hesitate to contact itch for a refund. If too many people are having this problem and no one can help me to figure out how to fix it, I might just have to scrap the Mac version entirely :(
Sorry for the trouble and I hope you have a good weekend despite this :3