Go to Settings> Advanced features> Side button> Double press> Select modes and routines. You'll be able to double press your power button to access your mode or routine.
Or just go to your widgets menu and select modes and routines widget and add to your home screen.
I think you can achieve this with modes. Open Modes & Routines, create a new mode, give it a name, configure it and save it. Leave the the Turn on automatically empty.
Then, swipe down from top of the screen to open the notification panel & swipe left. Select Modes.
Select the newly created mode on the pop-up list to manually activate it. Repeat same to deactivate it.
