Screen shot key shortcuts don't work on Magic Keyboard

Greetings MrTimWarren,

Thanks for posting in the Apple Support Communities.

We understand you're able to use keyboard shortcuts with the built-in keyboard, but not the Magic Keyboard, right?

If we have that correct, let's check that these aren't disabled when you're using the Magic Keyboard. Use the steps below to review the settings to see if this could be related, and you can find additional details here: Use macOS keyboard shortcuts - Apple Support

Disable a keyboard shortcut

Sometimes an app’s keyboard shortcut conflicts with a macOS keyboard shortcut. If this happens, you can disable the macOS keyboard shortcut.

1. On your Mac, choose Apple menu  > System Settings, click Keyboard  in the sidebar (you may need to scroll down), then click Keyboard Shortcuts on the right.

2. In the list on the left, select a category, such as Mission Control or Spotlight.

3. In the list on the right, deselect the checkbox next to the shortcut that you want to disable.

If that doesn't clear this up, let's try forgetting the connection with the keyboard and Mac to establish a fresh connection. We'll be able to isolate if there may have been an unexpected occurrence happening by establishing a new connection. For assistance with forgetting the connection via Bluetooth, check out the steps here: Connect a Bluetooth device with your Mac - Apple Support

We hope this is able to help. If not, provide more details on the steps you've taken so far, and include any additional information that you think could be helpful. We'll gain a better understanding of what could be occurring to work with.

Have a great day!