I assume you’re at home? Also, every other website you visit is coming up, no problem.
I would bring up a command window and type in “ipconfig /all” and make sure your IPv4 address, subnet mask, gateway, and DNS addresses are right. Your default gateway should be the address of your home router, say 192.168.0.1 (but there are other popular addresses that your ISP defaults to.) Your DNS will probably be the same your gateway, but again, your ISP may point you to their DNS server located in your local data center. 8.8.8.8 or 1.1.1.1 are popular 3rd party DNS servers, too.
Subnet masks are usually 255.255.255.0 for home networks, which provides for ~250 local IPv4 Addresses for your home. Your device’s IPv4 address should have the first three numbers match your Default Gateway (say 192.168.0.14).
Assuming you didn’t make any changes to your router, the network information about the router should be on a label on the router.
I have a Synology router which has a malware filter that blocks URL’s. There was some module that XenForo was using that got blacklisted (old certificate or something) so I was getting a similar “Site is Unavailable” but nothing was telling me that my Router was “Saving” me from SatelliteGuys.
When you’re using your VPN, your traffic bypasses any local router influence.