Update on the friend whose Nextcloud install I could simply not work out on his Windows Server:
Finally convinced him to accept Linux as his lord and savior.
Installed Nextcloud and had it running for him in half an hour.
The previous owner (or maybe just Windows Server itself) had shit running on it that was blocking 443. Couldn't find it. Some webserver, somewhere, but getting Windows to tell you what service or process is using a port requires thumbscrews and waterboarding. Cloudflared was also being blocked by something (didn't even know that was possible). Anyway. Hope that's the last time I have to use that OS. Probably won't be.
