It may seem obvious, but do you have IMAP enabled for the affected account? You need to check this first and foremost. There have been cases of IMAP not being enabled for Gmail accounts when the assumption is that it is enabled.

Hi, thx for reply. Yes IMAP is enabled. On my other laptop, the account in question works perfectly using IMAP, but not my current machine. So, I'll just have to live with it. Disappointing but reality. Thx

You could simply copy the Tbird profile from the other laptop to this one.

Oh yes, I didn't think of that! I'll search for instructions to do that.

Thx

See Profiles - Where Thunderbird stores your messages and other user data

Thanks for reply. So, it seems the version running on my old machine is FOSSAMAIL - which I believe is a T Bird derivative. The instructions for capturing the PROFILE I want to copy, do not match up with the instructions in the link you posted for PROFILE copy/capture.

In FOSSAMAIL - I can get to APPLICATION BASICS - SHOW FOLDER (local drive)....then it differs. Opening the FOLDER does not produce/display a profile string or similar. Right clicking 'SHOW FOLDER' produces 'RELOAD' or SELECT ALL' not a save or copy command. TIA for any further assist..

Fossamail is not Thunderbird. Simple as that so any knowledge you need to fossamail will not come from this site, folks here use Thunderbird.

The issue may be as simple as you have disabled cookies in Thunderbird. Up until February Thunderbird did not use oAuth authentication of POP. It now uses oAuth by default for IMAP and POP, but it requires cookies to function. oAuth does not require fiddling with the allow less secure apps setting, wich Google are phasing out of existence starting with gsuite.

So the procedure is.

• Check the Gmail web site to ensure Thunderbird is not a prohibited application is the allowed third party programs part of googles account settings. Clicking no just once puts it there.
• Check that IMAP is enabled, per the Google web site.
• Ensure you are not using a VPN. I am not aware of a single commercial offering that actually works with a mail client out of the box.
• If you have an anti virus product other than defender, ensure is is not set to scan email, and that Thunderbird is allowed in the firewall component. Note here that validation of oAuth occurs using web protocols on web ports, so anti virus product are prone to block non browsers doing things on those ports.

Some clues around the account setup. If the wizard reports it is unable to get settings for Google you have issues with connectivity. Gmail's settings are stored here. So should be detected in ALL cases. If they can not be verified then you have issues most usually with the firewall or anti virus on Windows. AS lots of folks are using the automatic settings, the problem with correct settings not working is a local issue.