I think we need some more detail about what problems you're having. I have no experience with Mailfence, but I have the current Thunderbird and Gmail working perfectly together -- no problems whatsoever. Tell us more, please.

I cannot just enter my name, email, & password any longer, as Thunderbird tells me it needs imap or pop info & port as well as smtp info and port.

Yes, that is part of the info needed to set up the account.

Where do I get the information needed?

I have attached the screen which comes up. However, I have searched the gmail settings in Thunderbird and the ones I have found do not work.

Thanks for your help!

You get the incoming (IMAP or POP) addresses and the outgoing (SMTP) addresses from the Mailfence and GMail sites. The necessary ports to use and the security settings will be found at the same sources.

Google "setting up a GMail account" and "setting up a Mailfence account" if you can't find the addresses, ports, and security settings at GMail.com and Mailfence.com.