You may remember a similar thing happening not long ago. Google insisted that POP3 mail accounts were, “not secure enough”.
So, you had to go through a convoluted process on Google to enable “less secure” Tbird to play nicely with POP3 for Gmail.
Right. Now, Gmail will effectively shut off POP3 completely for Thunderbird users by May 30, 2022.
So, how do you fix it?