From yesterday Thunderbird cannot get my messages.
Error message: Could not connect to server 127.0.0.1 connection refused.
I have checked all the connection setting. I cannot find the problem.
I have Windows 10 and Thunderbird 91.4.1
I ran your error message through Google; you may have done so as well. I'm not at all sure that this is a Thunderbird (or Plusnet) problem.
Other people seem to have had this sort of problem in the past when it seemed to be related to an interaction with their antivirus package (the case that I found was AVG). What anti-virus package you are using? It might be worth popping over to their user-group (if they have one) to see if others are reporting the problem there.