The CORS errors are just failures to fetch Nip05 IDs from sites that won't accept requests from a web app. You can ignore those.

The likely reason you can't access NostrGram is because it's running off a web socket server on port 444. If you have a custom configured firewall it won't allow the request. Check your firewall and see if that port is open. On standard Windows/Mac/phone firewalls it is, but more advanced users might have more advanced lock-downs.