I deleted what I wrote before. If it federated, ignore it.
Your browser is trying to find startpage.com on your local machine instead of the Internet.
While on the VPN, open a command window and ping startpage.com. Does it return localhost or the real IP address? If it returns the real IP address, then the problem is related to the browser. Try another browser to see if it's Vivaldi-related.
If it returns localhost then maybe it's a setting in protonVPN?
This is strange. Just try to find clues.