Press Ctrl+Shift+F for Classic Search or Ctrl+Shift+K for the Quick Filter Bar.

Ctrl+Shift+F works but how do I get it back on to the task bar? I very seldom use the Quick Filter Bar and having to use the multiple key hits is annoying.

This just seems to be another improvement that isn't.

As far as I know there was never a "search messages" available on the Thunderbird toolbar. David do you recall such a thing?

(And certainly nothing on a Windows task bar.)

The Phoenity Buttons add-on adds a Classic Search button to the tab bar.

Maybe I should have said Quick Filter bar. Up until recently I had 2 at the top of my screen. The one that is still there and accessed by Ctrl+Shift+K. There was also one present, on the main TAB where all my email accounts and folders were, at all times which allowed me to search/filter whatever mailbox I was on/in. That now seems to only to be accessible by Ctrl+Shift+F. This is a pain for me because of arthritis in the hands. Is there a setting that would keep this visible as before?

Why does it seem that every time there is an update some other useful tool or feature is lost or replaced by something less useful?

Is global search disabled? in options search for global. I ask, because I am not aware of any supported way to actually remove the search box from the toolbar short of disabling the global search and indexer.

But, in attempting to remove before I posted my denial, I got a not possible icon on my mouse, but when I dropped it it did disappear from the toolbar. So I guess there is a bug in there somewhere.

So right click the windows titlebar / toolbar and select customize. Drag the search icon back to the bar and save.

My global search option is on. There is something weird here though. When I use Ctrl+Shift+F a new window pops up and allows me do do the search I want. When I click on the search bar on the App's tool bar i get results from all folders and accounts. However today I accidentally pressed Ctrl+Shift+K and what appeared on the main tab was the search bar I used to have and it is persistent. So I guess I can say "Problem Solved".

ctrl+shift+F is (the original) Search Messages (Edit > Find) - searches an account's folders. Or potentially more, if you save it as a virtual folder / saved search.

ctrl+shift+K is quick filter - operates only on one folder

ctrl+K is global search - operates on all folders which have been enabled for indexing to Global Search (Settings > Indexing)