I have been using Thunderbird for about a decade or more. I am a seasoned email user. I have registered personal domains and upon them have custom email addresses for everything I do on the Internet. Every bank, creditor, merchant, etc., has its on custom email address on one of two domains. When it comes time to check email on the Thunderbird Windows desktop client, I always check one specific email mailbox first, then a second one, and finally to a Get All Messages.
This behavior of mine has always been possible by the fact that the Get Messages button had a drop-down menu that allowed me to select a specific mailbox. The latest update removes this functionality and presumes no one has more than a single mailbox account. Or worse, Mozilla dev crew thinks advanced users have not customized their json file so there is a single Inbox covering many mailboxes.
This reduction in functionality seems to me, an older power user, to be akin to the Microsoft development movement, which is to remove functionality. I've already eliminated Windows 11 from my home and any new PCs will be on Linux builds. Now I have to find another email client because mozilla has taken on this give them less in a product. Shame on you!