I was having a very similar problem to letum00 and adaughe2. Can't access the Unraid web UI via the Tailscale FQDN. I figured out that adding in the Tailscale TLD as the domain Unraid is running under (Settings > Management Access > Loacl TLD == my-domain.ts.net) fixed the issue. I don't love this as it means I can't access via a PC not running Tailscale anymore. No, I did not have any subnets setup.
Any idea why Unraid is binding specifically to the hostname specified in the settings page? Is it doing some kind of hostname validation on the incoming HTTP request?
edit: I'm pretty sure I'm actually hitting this bug -