how do I connect my Mac and iPhone and iPad togather
how do you link Mac, iPhone, iPad to gather and to be able to use the iPad as a second screen
MacBook Pro 16″, macOS 11.2
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An iPad Pro can be used with a compatible Mac to extend the Mac display to the iPad using the Catalina/iPadOS Sidecar feature.
https://support.apple.com/en-gb/HT210380#systemrequirements
An alternative third-party product, Duet, can be used to extend a PC or Mac to an iPad: