Create an exception in your anti-virus software for the Thunderbird profile folder, so that the anti-virus real-time scanner will not scan it. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data#w_how-to-find-your-profile

Thanks for the suggestion. I don't use any virus scanner software other than Windows Defender. I found a place in Defender where I can allow the Thunderbird app through the firewarll. Maybe that will take care of it.

Open Windows Security, select Virus & threat protection, Virus & threat protection settings, Manage settings, Exclusions, Add or remove exclusions, Add an exclusion, add the profile folder whose default location is:

C:\Users\username\AppData\Roaming\Thunderbird\Profiles\1234abcd.default or 1234abcd.default-release

or copy from Help/Troubleshooting Info, Profile Folder, Open Folder.