Mac Mail/Settings Won't Open Gmail Authentication Window in Safari

Opened my computer one day and all my gmail accounts coming through to my Mac Mail would no longer work (despite the fact that I hadn't changed anything on my laptop in days, and those same gmail accounts continue to come to my phone just fine). When I try to take all the gmail accounts back-online a message box pops up saying "Google requires completing authentication in Safari. After authentication, set up will continue in Internet Accounts." When I click "Open Safari" a blank page loads in Safari, and that's it. When I open my gmail account in Safari, email appears to be working just fine, but I can't seem to find a way to authenticate my Mac Mail. Any ideas on what's happening here? I've tried deleting and re-adding the accounts, but the same message box pops up and won't allow me to authenticate in Safari, so I can't re-add the account. I've also tried turning off two-step authentication and setting google to a lower security level to try and work around this new authentication step, but no dice. Would SO APPRECIATE any help with this!

OS: Mojave 10.14.6

Safari: 13.0 (with pop-ups enabled)