I won’t go into a long and dramatic explanation of the differences between POP3 and IMAP. Convert your POP3 Gmail setup to IMAP in Thunderbird

Nevertheless, there’s not much you can do about it. This is not happening for your safety and security. So, sure – OAuth 2.0 is all whiz-bang secure, but don’t kid yourself. I mean, this is the company that gave you a 1GB storage space with your brand new e-mail account years ago – as long as you agreed that they get to read all your mail. Honestly? Because Google wants to spy on you better. Your only option is to switch over from POP3 to IMAP in Thunderbird. This time, there isn’t an option to make it work anyway with Gmail. Now, Gmail will effectively shut off POP3 completely for Thunderbird users by May 30, 2022. So, you had to go through a convoluted process on Google to enable “less secure” Tbird to play nicely with POP3 for Gmail. Google insisted that POP3 mail accounts were, “not secure enough”. You may remember a similar thing happening not long ago. If you use Thunderbird to download e-mails from your Gmail account, it may stop working soon.

Configure thunderbird for gmail