macOS Mojave 10.14
Use the stylus as a pen or mouse in Ink on Mac
Use the Ink toolbar to switch between using the stylus to write and control the pointer.
In the Ink app on your Mac, do one of the following:
Tap the first icon in the toolbar of the Ink window to toggle “write anywhere” on or off.
Click Ink (if shown) in the menu bar, then choose Write Anywhere to use the stylus as a pen. When the command is not selected, the stylus is used as a mouse.
If you have a Wacom graphics tablet, use the Wacom Tablet app to set up the stylus. For example, if you assign the Command key to the first button on the stylus, you can hold that button while writing Q to quit an app.