>
> I'm using dovecot-2.3.17.1-1.fc34.x86_64 on fedora34 and Thunderbird 91 on
> fedora35. When creating a folder of type "folders only" in Thunderbird,
> then trying to delete it, it doesn't actually delete it from the
> filesystem. Is this a permissions problem? Or perhaps a Thunderbird problem?
>
> I don't see any messages in the logs that would indicate some type of
> failed attempt to delete. How do I troubleshoot this?
>

What do you get from the following command?
(Substitude the shell variables with your case.)

doveadm acl rights -u ${YOUR_USER} ${FOLDER_NAME}