I have the tag function as in the picture in 132. Do you use any add-ons that have something to do with bookmarks? I couldn't find an option that affects this either. Not even in about:config.
I found 3 solutions, all of which have the same solution. You should enter a bookmark tag in the Bookmarks Manager so that this appears. It's probably a bug since Firefox 116. Solution 1, Solution 2, Solution 3.
Now it remains to be seen whether it will work for you.
Edit: Have linked solutions.
You don't have to do anything. K-9 Mail remains K-9 Mail. A mistake was made in the naming process. This will be fixed soon. So in F-Droid the following will be present: K-9 Mail Thunderbird Thunderbird Beta
Thunderbird for Android is based on K-9 Mail, but has received a few changes here and there (e.g. the accent color is blue instead of pink). As mentioned above, K-9 Mail will remain and will probably continue to get the Beta & Stable versions in the version selector. Thunderbird has been split into two apps for this purpose. The settings should usually be able to be adopted from K-9 Mail and vise versa, because of the same codebase (but I haven't tested it). In the end, it's up to you whether you prefer the dog or the bird. :)
Edit: Added more info.