An operating system

If you already have Nextcloud running you can use the Nextcloud Forms app

Honestly, I would say because you just have less struggle. I had just a lot more problems when I was using Ubuntu instead of Debian. But I thinks it’s mostly personal preference

I don’t know about photoprism but I guess that’s not going to work because it’s really hard to provide features like face recognition and a web frontend with a zero trust setup. So if you just want the to have a automatic photo backup you could take a look at encrypted folders for nextcloud

Just in case you never heard of it, there is also the option to use Tailscale. It lets you connect to your services without opening any ports and uses Wireguard under the hood but makes configuration simpler

Maybe you could also try to generate your one SSL certificate and add it to your Android/Linux/Windows devices as root certificate 🤷🏼‍♂️.

That’s only a possibility, of you’re willing to do this to every single device that should be able to connect to your services