Dovecot is on version 2.2.36. I tested it. Outlook on the Apple system successfully logged in with the imap protocol, and then sent the LIST command and outlook did not send any further. Dovecot returns the results as follows:

A003 OK LIST completed (0.001 + 0.000 secs).

There is no problem with version 2.1.17 using dovecot before. The information returned by dovecot in version 2.1.17 is as follows:

A003 OK LIST completed.

I suspect that the feedback of the following information causes Outlook to not recognize it normally:

(0.001 + 0.000 secs)