On a Mac, Cmd takes the place of Ctrl in every shortcut below.

Anywhere in the app

Ctrl+K opens the command palette, a search box over every destination and setting.
Ctrl+B collapses the sidebar to icons, or brings it back.

Backtest and Optimize

Ctrl+Enter starts the run. On Optimize, pressing it again while a sweep is running stops the sweep; Backtest has no in flight stop, so it does nothing while one is running.
Ctrl+P opens or closes the settings window under Settings on the run bar, so a value can change and the run repeat without losing the result on screen. Held off while a field has focus, so a parameter you are typing keeps every keystroke.
Escape closes whichever window or menu is currently open, the settings window among them.

The Backtest replay

Once a run carries step data, replaying it bar by bar adds two more, held off the same way while a field has focus and active only while the transport is on screen:

Space plays or pauses the replay.
Right Arrow steps forward one bar at a time.