[lomkiri]

Calibre 5.99.8 (beta for the forthcoming 6.0), debian bullseye :

1) Really, we have to select the area before to click on trim button, but it seems to be a feature (1srt: select the region where the filter ('trim' or another one) will apply to / 2nd: select your filter) more than a bug. It may be surprising at first use, but once we know the process, no pain at all.

I prefer the present way, since when you release the mouse button after selecting, you are still able to redim the selection, and when you're ready, you click on "trim". The way you are proposing, you would have no chance to redim your selection.

2) undo is working okay here with Ctrl-Z, or with undo button on preview window, or with general undo on main toolbar.