The transform tool is not available again via pressing Ctrl + T after the leaving of the transform tool by pressing Esc or by pressing Enter. The leaving of the transform tool forces you at first to press "T" to switch to the move tool for the further activation of the transform tool via Ctrl + T.
You only have to click on the canvas again to the get the transform tool rectangle back, you don't need to switch tools.
You are right. Sorry for my unawareness. Nevertheless it is so tricky to find this answer. Why there is not the occasion to do so by the alternative way for example via pressing Ctrl + T again? The general thing in Krita is the lacking of the alternative ways to do a task by the user. This limiting feature forces the users to read the all manual. It is not comfortable for the many users.
Huh, the usual complaint I get is that there are too many ways to to do the same thing, not that Krita is lacking alternative ways to do a task.