Dual screen with 2 laptops

Well no, between the two there is a graphics card, and its main purpose for a graphics card is to generate output signals. For input signals, you have dedicated modules, a video capture card. But even with a good capture card, you're not sure you'll be able to display what you want to do, given the number of restrictions imposed on copying.

I just found MaxiVista, it works perfectly.

Thanks again for your "helpfulness".

"Is there no way to link them?"

The two PCs, yes... but for data transfer! Not for creating an 'extended desktop' on the two screens!

"Technically, it's just a display 'attached' to a keyboard/system."

Yes... but have you seen what carries the video signal to the screen?! A thin ribbon plugged into a specific connector on the motherboard. In other words, the laptop screen only receives an image from the motherboard (or through it), and never from an external source.

"I just found MaxiVista, it works perfectly.
Thanks again for your 'usefulness'.

You're welcome... we also appreciate the bullshit.
https://www.commentcamarche.net/infos/25855-charte-d-utilisation-de-commentcamarche-net-respect-d-autrui/#respect-d-autrui

Your information is wrong, so instead of shouting that it's a scam, refrain from responding.