Use buttons on stylus as shortcut

Apple Pencil

For Apple Pencil, you may double tap to switch between eraser and your last selected tool.

Samsung S-Pen (Air Actions)

Open your device's Settings > Advance Features > S-Pen >Air actions.
Tap your desired app under Air actions.
Find and tap Notewise. Make sure it's turned on. You can also customise actions for different gestures in the popup.

To learn more, here's a video tutorial from Samsung on Air actions.

Xiaomi Pen

To switch to eraser, click the primary button on the pen.
To switch to the previously selected tool, click the secondary button on the pen.

OnePlus/Oppo Pen

You may double tap to switch between eraser and your last selected tool.

Vivo Pen

Note that this only works on Vivo pens later than Vivo Pencil 2 / iQOO Pencil.

You may double tap to switch between eraser and your last selected tool.

Lenovo Pen

Note that this only works on certain Lenovo pens, e.g., Lenovo Precision Pen 3, Lenovo Tab Pen Plus

To switch to eraser, click the primary button on the pen.
To switch to the previously selected tool, double click the primary button on the pen.

Huawei M-Pencil

You may double tap to switch between eraser and your last selected tool.

For this to work, Make sure to disable stylus shortcut in Settings > Accessibility features > Stylus > Double-tap, make sure that "Open shortcut menu" is de-selected.

EMR stylus

For EMR stylus with an eraser button at its end, you may use the eraser button to perform erase action.

Long press to switch to eraser

On some stylus pens (e.g., Samsung S-Pen, Lenovo Precision Pen 2), when the stylus is close to the screen, you may long press the primary button to switch to eraser.