How do I connect a Mac Studio to an iMac through AirPlay

I am trying to make an iMac 2017-model work as a second display to my Mac Studio M2 and Studio display. The iMac sees the Studio, but the Studio does not see the iMac. The Studio sees the MacBook Air M1 with wireless, and can use the MacBook as a second display. All computers are connected to the same network, and uses the same administrator login. The Studio can be set to share the mouse and the keyboard with the iMac, but to start up the iMac, only mouse and keyboard connected will work. After login, I am able to control both computers with one keyboard and one mouse. Still I cannot move windows from the Studio to the iMac. It is possible to connect the other way around. The iMac sees the Studio, and the Studio display work like a second screen. This can of course be done by just connecting the Studio Display to the iMac, so no real point in this. What I need is to connect the Mac Studio to the iMac making the iMac work as a second display. What can be the problem here?

[Re-Titled by Moderator]