In the setup I use I have the following 3 devices: iMac 27" late 2015 with OpenCore Legacy Patcher Sonoma: 14.1.1 MacBook Pro 15" late 2016 with OpenCore Legacy Patcher Sonoma: 14.1.1 iPad 10.2" 7th Gen with iPadOS version: 17.1.1 They are connected to the same WiFi network. Steps: On the iMac go to: System Settings -> Displays Click the plus sign to the right of the Built-in Display Choose under Mirror or Extend to: MacBook Pro Choose under Link keyboard and mouse to: iPad...

Install Windows on your iMac and use the software utility spacedesk. Such a simple solution to turn any iMac into a second (or even a third or more) display to extended your desktop.