Authentication failure with Outlook; no authentication popup

Hi all! I'm having an issue with Thunderbird in conjunction with my Outlook account. I used to be able to add my account just fine (using OAuth2). But for a few months now, I have been getting "Authentication failed" errors (see first picture). It used to be that I could temporarily remedy this by signing out and back in. Today, however, I was unable to sign back in, using the stock settings for Outlook (see second - fourth picture). No authentication popup appeared. I was sporadically able to add the account and get messages to start appearing by clicking on "Edit configuration" and removing and re-adding the hostname for the IMAP server, without an authentication popup appearing. I therefore suspected that there might be some half-stale credentials stuck in the cache, and there probably were, because after clearing my cache this method doesn't work anymore. I am still not getting any authentication popup though. All the usual suspects I already tried: Thunderbird is up-to-date (151.0.1), my Outlook account definitely has IMAP and SMTP activated, and another mail account (gmail) works without a hitch on the same system. I hope that someone can help me, as I'm at my wit's end. Thanks in advance!