I am using Thunderbird 140.6.0esr (portable), and I have found that keeping subfolders compact is essential for stability when moving the files between computers. At one time, there was a menu item for "Compact Folders" which would compact all subfolders in a subfolder, but that went away a while ago. What I have to do now is right click on every subfolder and click on "Compact". What I would like is a keyboard shortcut, and this exists for folders, but subfolders have two menu items that use "C": "Copy to" and "Compact". So I have to right-click, hit "C" twice, then enter. This gets very tedious when I have dozens of subfolders to compact.
Please change the subfolder right click menu to be consistent with the folder right click menu so that "C" performs Compact Folder in both.