synology has surveillance station, synology supports wireguard (tailscale, too), there's ios and android surveillance station apps.

The software that the synology uses on the backend is open source, so you could set this all up with proxmox or a debian server or something, too.

you need to ensure your cameras support either direct access inside the network, or onvif or something like that. IDK, i don't use it anymore, but i did for a good long while, with wifi and wired IP cameras. My synology had a "license" for 12 cameras, but lightning took it out (something about a bunch of ethernet cables in trees), and my new synology doesn't have enough licenses to bother with.

anyhow, just thought you should know - "software" "NVR" is available, and has been for over a decade.