Taken from hotkey summary in the Polaris manual.
Move to next object: Space-4-5 or F3
Move to previous object: Space-1-2 or Space-F3
Move to top of screen: Space-1-2-3
Move to bottom of screen: Space-4-5-6
Scroll down one screen: Space-3-4-5
Scroll up one screen: Space-1-2-6
Execute current item: Enter or Cursor routing key
Back button: Space-e, F4 or Space-Z
Move to specific object: press first letter of object name
Go to Home screen: F1
Activate App Actions Menu: Enter-I on focused app
Open Notification Shade: Space-1-2-3-4-5-6
Activate Notification: Enter
Delete notification: Space-D (dots-1-4-5)
Clear all notifications: Space-Enter-D (dots-1-4-5)
Activate Edit Box: Enter
Increase Slider Value: Backspace-Space-4
Decrease Slider Value: Backspace-Space-1
Double Tap: Space-Enter
Double Tap and Hold: Backspace-Space-Enter
Start/Stop Hold: Backspace-Space-Dot-2
Reset Polaris Launcher: F2-F3-1-2-3-4-5-6-7-8
Change object navigation method: Backspace-Enter-H (dots-1-2-5)
Go to next character: Space-6
Go to previous character: Space-3
Go to next word: Space-5
Go to previous word: Space-2
Go to next line: Space-4
Go to previous line: Space-1
Go to next paragraph: Space-5-6
Go to previous paragraph: Space-2-3
Go to beginning of paragraph: Space-1-3
Go to end of paragraph: Space-4-6
Go to top of document: Space-1-2-3
Go to bottom of document: Space-4-5-6
Delete current character: Space-1-4-5
Delete previous character: Backspace
Delete current word: Backspace-2-5
Delete current line: Backspace-1-4
Delete current paragraph: Backspace-2-3-5-6
Move to next display length: Down Scroll
Move to previous display length: Up Scroll
Open Main menu: Stop button
Recent Apps: Play button
Back: Record button
Move to previous object: Previous button
Move to next object: Next button
Android Media play/Pause: Hold Play button
Android previous track: Hold Previous button
Android Next track: hold Next button
Mobile Screen Reader on-off: Stop and Next buttons
Call Google Voice Assistant: Record and Play buttons