based mainly on this info https://docs.nextcloud.com/server/latest/user_manual/en/groupware/sync_android.html

• Log into your nextcloud at https://nextcloud.melm.xyz use the option to log in with “Authelia” you can use the same credentials you'd use at https://auth.melm.xyz
• Create an app password for nextcloud https://nextcloud.melm.xyz/settings/user/security
• Install the nextcloud client
  • Create app password to use https://nextcloud.melm.xyz/settings/user/security
• Sign in to nextcloud app using the password their should be a qr option in nextcloud web when you make the password (password is only shown once for security reasons

• Install https://f-droid.org/packages/at.bitfire.davdroid/
• https://www.davx5.com/tested-with/nextcloud