Drag a slider to set the font size of your notes.

You can assign hotkeys to any of these under Settings → Hotkeys.
If you use a toolbar plugin such as Editing Toolbar, add the Font Slider: Show font size slider command as a button. The slider opens directly under the button you clicked.
On mobile, where there's no status bar, use the ribbon icon or the command.
Font Slider makes no network requests and collects no data. It stores only your chosen size and range, in the plugin's own settings file.