Did you know that you can create custom keyboard shortcuts to toggle options such as Brush Pressure Controls for Size and Opacity?
To do so, choose Edit > Keyboard Shortcuts. Next to “Shortcuts For”, choose Tools. Then scroll down to the bottom of the list. To add a Keyboard shortcut to an item, click in the empty space to the right and tap the shortcut on the keyboard.
Note: the “K” and “N” keys are not assigned to any other tools (in Photoshop’s default Essentials workspace), so you might want to assign those first. And, the keyboard shortcuts for Tools are limited to a single key (i.e., you can’t add modifier keys like Command/Control or Option/Alt).
While you’re in this dialog, be sure to check out the other options that you can assign shortcuts to including the Mixer Brush and other options like Airbrush mode!