I mentioned a while back that I purchased a 2021 iPad Pro and Logitech external keyboard. This is a little hint to others who may have an external keyboard with a CMD key.
If you press and hold the CMD key for a couple of seconds, a Help screen appears and shows keyboard shortcuts available using the CMD key. The shortcuts are app specific, so you'll need to try this method within the different apps you use.
The Help screens often have different categories that you navigate by scrolling horizontally or tapping a category along the bottom of the Help screen. Help screens can be different within the same app, depending on what you're doing. For example, the Mail Help screen while reading an email is different from the Help Screen when sending a message. To save space, the Help screen utilizes the "looped square" symbol printed on the CMD key.
Below is a screenshot of the CMD Help Screen with available options while reading a message. Notice the black outlined arrow beside the get All New Mail option. That indicates the Shift key, so one would press Shift+CMD+N to activate this shortcut. Also, notice the various categories across the bottom of the Help screen.