How can I use mouse to move inbetween iPad and laptop

iPad is not currently capable of offering an “extended desktop” experience - such as that to which you may be accustomed on other computing platforms. The Mac Sidecar feature provides limited scope to use iPad as Second screen from Mac - but not the other way around.

Your iPad can drive an external display using AirPlay - or via HDMI (and appropriate adapter where needed) - but neither can re-scale the iPad output to match the native resolution of an attached monitor.

There are some iPad Apps in the App Store that provide some external connectivity options for PC and Mac (such as Duet and Duet Pro). These can be expensive - and have mixed reviews.

Here is a third-party comparison of some of the options - including a detailed look at SideCar.

https://thesweetsetup.com/apps/best-app-for-using-an-ipad-as-an-external-display/

A little hard to advise and help you when you provide NO information about your iPad.

Here are my questions to you.

What year and model iPad do you have/own?

The “A” model number can be found on the aluminium back of your iPad, in small print, right under the larger bold print “iPad”.

What iOS/iPadOS version is this iPad, currently, running?

Are you running the iPadOS 15 beta software and the new iPad/desktop integration feature ( Universal Control )?

Are you attempting to use the SideCar feature of iPadOS/macOS on a Mac"

What are you, exactly, trying to attempt with your iPad?

Please attempt to answer all questions asked.

Thank You.

This is how the SideCar feature works.

Yo use touch/Pencil or mouse with iPad, but cannot use mouse with two devices simultaneously, currently, as a separate mouse/trackpad can only be paired one at a time.

You must use a mouse with your Mac and a mouse with your iPad.

This behaviour will change when iPadOS 15 is introduced in the Fall of 2021.

The Universal Control feature will let you be able to use the same mouse or trackpad across iPad, Mac book, iMac simultaneously.