Thanks for the feedback! A couple of things that might help right now: you can tap a running action to cancel it mid-way, it won't refund the time spent but it stops further resource use immediately. For the lag, the game throttles rendering to save battery so there can be a slight delay between tapping and the UI responding, especially on older devices.
The pause idea is noted — a full time-pause is tricky in an idle game (the whole genre is built around time passing), but a quick "cancel current action" button that's more prominent is a fair ask and something I'll look at for a future update.
Appreciate the detailed feedback!