You’ll have to use http://192etc:port. So no httpS for internal access
This is not really correct. When you use http this implies that you want to connect to port 80 without encryption, while using https implies that you want to use an ssl connection to port 443.
You can still use https on a different port, Proxmox by default exposes itself on https://proxmox-ip:8006 for example.
Its still better to use (sub)domains as then you don’t have to remember strings of numbers.
Another +1 for restic. To simplify the backup I am however using https://autorestic.vercel.app/, which is triggered from systemd timers for automated backups.