Open Classic Search (Ctrl+Shift+F), click the Subject button, Customize..., add Message-ID as a custom header so it appears as a search rule under Subject, Date etc.

At one point it was possible to make a link of the message ID, click the link, and it would open Thunderbird and go to the message. Using Classic Search you need to have an idea where the message is. In my case, I have a very large number of folders in several accounts, which makes this hard. But in previous versions up to some point, the clicking on the message ID link worked fine. I've been using cb_thunderlink lately, which works, but clicking the message ID link is a cleaner way to do it, so I was hoping there's some way to make that work again other than Classic Search (or Global Search, where it also doesn't work anymore).

Thanks for your response, by the way.

The other add-on that finds a message, given the ID:

https://addons.thunderbird.net/en-US/thunderbird/addon/open-by-message-id/

Thanks again. I have tried open-by-message-id. As far as I can tell, it only works for cases where there is a message ID in a message body (or header). But the way I use it is to convert a message I'm interested in to an event, which inserts the message ID in the event, and then use the message ID in the event to locate the message in whatever folder I've filed it in for later. So the message ID is not in the body of a message to use this add-on with.

cb_thunderlink works (fitfully) for me, though.