USB tethering between home server and cellphone with cheap data plan. Setup iptables rules/default routes on the server and other devices on my LAN, to route traffic to the Internet through the server and the USB modem/phone. Call ISP and wait 3 months for them to unfuck phone/fiber pole trashed by tractor. Keep paying for service while it is down. Keep calm and carry on, at least I got a backup Internet access.
I don’t need to access this server from outside (and it wouldn’t work as the mobile Internet plan uses CGNAT), just to have the laptop or phone on the same LAN once in a while to let Nextcloud sync do its thing (essential files, Keepass database…). I suppose I could set up a wireguard tunnel between the home server and my cheap VPS, and access it from there, I just don’t have the need for it.