At the top right of the Thunderbird window, click the menu button ≡ > Settings > General > Account Hub Uncheck the box 'Create accounts in the new Account Hub'.

Thank you, but I tried that and it didn't work. I went back to 140.3.1est and use tbsync. My intent is to change to thundermail when it becomes available and drop my outlook.com account. Microsoft has become too pushy with their cloud-based ecosystem. Probably easier for most people, but I prefer having things under my local control.

If you're setting up your Outlook.com account directly in Thunderbird, just open Thunderbird, go to Account Settings > Add Mail Account, and enter your Outlook email address and password. Thunderbird will automatically detect the server settings. Make sure to select IMAP so your emails stay synced.

Step 3 of the instructions I referenced above say that I should see a button labeled "Exchange" but I don't see that. The point of my question is that I want to connect using the Exchange protocol, which is supposed to be implemented in TB 143.0.1. The Exchange protocol includes calendar and contacts, which are not yet available in TB. Unfortunately, I need a client that includes those, so I will need to wait until those are implemented in TB. But thank you for taking the time to comment.

I believe that I have found the answer to my problem. Apparently, Microsoft does not provide the Exchange protocol for connecting to Personal or Family subscriptions to Microsoft 365, only IMAP and POP. On the other hand, Provider for Exchange ActiveSync allows TbSync to access my outlook.com calendar and contacts, so I'm not sure what's going on. Neither of these add-ons have been updated to TB 144 yet.

Administrators of business and school subscriptions can enable Exchange connections. Unfortunately, Mozilla's instructions (linked in my original post) seem to assume such an outlook.com account.