A good idea would be if someone would make an add-on for home finance, a maked a program for android!
You can always sync your Gnucash or Quickbooks or whatever other files with Nextcloud, but otherwise I can’t see how finance falls within the scope of Nextcloud at all.
If you want to give it a crack, start here: https://docs.nextcloud.com/server/12/developer_manual/app/startapp.html
But the world of finance is more complicated than it seems…
I suggest you QuickBooks for small business. If you need any help just visit here
If you are still searching: finance android app with WebDAV sync: