Mine is using the arrow keys to navigate typed text while writing and editing. It helps speed things up, versus having to move your hand to the mouse to navigate.
Use the Up and Down Arrows to move/jump vertically.
Left and Right Arrows to move/jump horizontally.
Combine Left or Right Arrow with Shift to be able to select text. Use Up or Down Arrow with Shift to quickly select whole/nearly whole sections of text.
Combine Control with Left/Right Arrow to jump whole words to more quickly move to where you want to type.
To be pedantic, keyboard shortcuts aren’t hacks. That’s the intended use of the thing, and long lists of keybaord shortcuts exist so that people can find the ones that work for them and use them. Just because most people don’t do it doesn’t make it a hack.
My favorite keyboard shortcut is Super/Windows key and spacebar switches keyboard languages. That’s not a hack, though.
Closer to a “hack” is going into an android phone with ADB and disabling bloatware manually.