If all else fails, open port 22 and sftp text files back and forth like the good ol days.
Oh, nvm you were looking for office like collab. I don't use it personally, but NextCloud comes to mind. I don't think any coding is necessary, but it requires manual set up either at your home or on a linode server/cloud hosting.
https://nextcloud.com/install/#instructions-server
https://www.linode.com/docs/products/tools/marketplace/guides/nextcloud/
Discussion
I don't know how to do that, but I suppose I could figure that out. There's no encryption on those files, though, if they are plain text...
Sftp is encrypted. I use it to sync files on my phone from my home Synology nas with the FolderSync app.
I was thinking about using NextCloud for it, but I went with the simplest option for my needs, since I'm the only one using it. It's a fairly low level solution.
Oh! I use syncthing for a few folders to keep things current between my phone and laptop. If it's like that, then it's really useful.