using an iMac as a monitor for a MacBook Pro

I have a late 2013 21.5 inch iMac. I've just bought a new MacBook Pro 13 inch. Rather than buying a monitor I'd like to use the iMac as a monitor. I believe this was possible with older versions of software, maybe not Catalina, the version I have.

Does anyone have a suggestion as to whether this is possible?

thanks

Don