If you are using a VPN app it may be intercepting and proxying web traffic for you (whether you realize it or not). This would explain why it works when you ‘turn off the vpn’.
If your VPN provider requires an app, well, that sucks and you should consider using another provider that does not.



Raspberry Pi’s are full of possibilities, even old ones. Here is what I’d do.
Not sure what you mean here but there is no reason that any modem or WAN box ever really needs to involved with a pi-hole. You can set the IP to use for DNS lookups on each host by hand… OR you can turn off DHCP services on the modem run that off of the PI, which then sends the IP of the PI/PiHole for DNS as part of the DHCP lease to each client.
At any rate, ideas for it:
There are so many more ideas like weather stations, news feeds, little web services for whatever.