Also I have enabled this ( and again, I do not have the issue with other 3rd party email managers): https://www.xfinity.com/support/articles/third-party-email-access

and I also have cookies enabled.

The issue remains, cannot add comcast email.

Not sure if part of the issue is related to the settings defaulting to OAuth2 instead of Normal password (neither work), perhaps OAuth2 is needed but no login popup ever happens?

I think that, in addition to enabling third party access, as described in the article you linked, you're supposed to set up the account in Thunderbird as described here:

https://www.xfinity.com/support/articles/email-client-programs-with-xfinity-email

Post a screenshot of your account settings if that doesn't work and you're unsure whether you've setup the account in Thunderbird correctly.

I think that, in addition to enabling third party access, as described in the article you linked, you're supposed to set up the account in Thunderbird as described here: https://www.xfinity.com/support/articles/email-client-programs-with-xfinity-email Post a screenshot of your account settings if that doesn't work and you're unsure whether you've setup the account in Thunderbird correctly.

So I have tried both the mozilla thunderbird and the "other" instructions.

1) Mozilla Thunderbird That xfinity page links to here: https://support.mozilla.org/en-US/kb/automatic-account-configuration

and Step #4 ("4. Granting Thunderbird Account Access") never happens despite Thunderbird defaulting to Oauth method.

2) Using "For other programs not listed, use these settings to connect your Comcast.net email:" instructions, it simply does not connect, I have followed it carefully, the comcast email does have third party permissions enabled, and Microsoft Mail app works with these settings so I know it is possible.

Also to note, troubleshoot mode, reinstalling, did not help. I am on ESR version 128.7.0 64bit as well.

The generic config settings for other mail clients is the reason I linked the page, so if you post a screenshot of the settings you're using, we may verify they're correct, because missing something there is by far the most common cause of this kind of problems.