Can't set up xfinity email account on Thunderbird

New PC, using Thunderbird Windows 11. Xfinity blocks me as I try to log on to complete the setup. "Access Denied. You don't have permission to access http://login.xfinity.com/login" on this server. I've spent ~2 hours on chat with Xfinity techs who can't fix the issue. Last week setting up wife's new PC, had same  problem, but tech fixed it. Everyone I chatted/talked with today seems to think I should change settings on the Account -- while I keep telling them there is no account yet as Xfinity won't let me set it up.  I see this problem in a post from 4 months ago, though no solution.