how do I connect two imac s running catalina?

If you are referring to Target Display Mode, that was discontinued with 2014 iMacs. In order to run TDM, if you have qualifying iMacs they both must be running High Sierra 10.13.6 or earlier. In short, you cannot use TDM in Catalina..

You can't, the last iMac that supported Target Display Mode was a Mid 2014 iMac.

see > Use your iMac as a display with target display mode - Apple Support

No sorry there is not, if you need an external display for one (or both)of your Macs, you need to buy one.