So, I use joiplay to play most of these games on my phone and I used to play this game windows version on my phone using joiplay as well because I just prefer to have the whole game that is not separated into two parts but it doesn't seem to work with the last few versions. Does anyone know a solution to this?
Yes, you're right. The latest versions don't work for me either. I haven't found a solution among plugins or settings. I made no technical changes on the PC between versions; only the file size increased due to new content. And on the JoiPlay Reddit, they write that some games are just not supported.
You should still try to play the split versions. I have made an automatic transfer of saves between versions, so the transition between versions will be effortless and lossless. Also, if you still have saves from JoiPlay, you can also transfer them. To do this, start the mobile version of the game to create a save folder. Then, transfer your old saves to the Android/Documents/WaifuSlutSchool/saves folder.