Um.. I want to ask, is your game using NW.js or Electron.js?
If you still encounter issues with full-screen mode, you can also try my recently developed NekoGakuen SteamworksPlus plugin, which I wrote myself. It's a bit different from NekoGakuen SteamworksAPI in that it doesn't rely on Greenworks.js and doesn't require downloading the corresponding version of node, etc. However, I've been very busy lately and haven't had time to use machine translation to translate the plugin into English yet...🙇♀️
Viewing post in NekoGakuen SteamworksAPI comments
Ah... oops... I forgot to correct that. Thanks for your report. Actually, at first I thought this could only run on Electron.js, but later I found out that NW.js could also use the plugin I wrote. Anyway, this plugin can now be used on both NW.js and Electron.js.
(PS. I didn't expect that I forgot to switch back to my itch account to reply..)