Alternative to Kijiji and FB Marketplace

Have you tried a different locations with your VPN? I use to have problems with PipePipe (a YouTube frontend) using my VPN in one location in my country, moved to another and has been fine for months. For example with Mullvad there’s 30 locations in Canada across 4 cities with 4 providers. Not sure about Proton but I imagine they have more location options, you could try a different location see if that helps. If no luck, you could test if its addy by trying duckduckgo or simplelogins aliases, they are both free so you could give them a shot. Other option would be to try a “trustworthy” public WiFi, for the account set up with an aliases if they are blocking know Proton IP addresses.