As stated in the posts above,
1) connect one monitor via HDMI cable - done here...
2) connect 2nd monitor wirelessly,
- go to laptop settings , sharing, check screen sharing
- go to iMac,
do one of the following:
- Connect using the name: Click the Finder icon
in the Dock to open a Finder window. In the Locations section of the sidebar, click Network, double-click the Mac you want to share, then click Share Screen.
If no items appear in the Locations section of the sidebar, hold the pointer over the word Locations, then click Show.
- Connect using the address: In the Finder, choose Go > Connect to Server, enter the address of the Mac you want to share, then click Connect.