IMAP support in new Outlook sucks as all other methods offered in New Outlook. MS just wants to synchronize your mail to MS cloud. You do not want this. You do not want all your e-mails sent/received by you favorite IMAP provider, company/private account to be stored in Microsoft. You would need space for the same thing in MS cloud, eventually paying it twice. I have 15 GB of emails in Gmail account. And MS wants me to let them to sync my Gmail to MS cloud? Really? Piss off Microsoft. New Outlook is just an attempt to get money from people and from advertising. You will not get mine. New Outlook is not a mail client, it cannot work in client mode for a handful mail servers. It is just one-purpose MS cloud mail viewer.
I lost my hopes this ever changes.