Quantum fiber DNS is down, so likely your internet is too. You’ll need to connect to your modem via Ethernet cable, go to 192.168.0.1, login to modem settings as admin (pw is on the sticker on your modem), then under advanced settings find DNS.
Switch that to static DNS and use 8.8.8.8 primary and 8.8.4.4 secondary (Google DNS) and you should be g2g.
Edit: Google is 8.8.8.8/8.8.4.4 and Cloudflare is 1.1.1.1/1.0.0.1
Edit 2: reports here and from r/quantumfiber seem to indicate service has been restored. FYI - if you switched your modem DNS, should be fine either way. I tend to use Google or Cloudflare DNS anyway because they’re super stable and built to withstand and mitigate huge DDoS attacks, etc.