wwe
3
I agree this is very strange uncommon but interesting requirement.
I think following discussions might be helpful for you
I think with lot of work you could achieve your goal if you
- first build the local network with internet connection so you can follow normal installation path e.g. request certificates
- setup split-brain DNS to access Nextcloud using local IP when inside of network (must be hosted on same Raspi)
- isolate and host all “internal” network components like DNS, router, firewall etc on your Raspi (or something you carry withyou)
- develop a procedure how to setup internet connection with DynDNS like service from time to time to refresh certificate (and perform updates)
I would call the project “local network to go”