Unity does allow to open many different projects running on the same engine version, so it’s probably possible to implement by the UE devs at some point.
Maybe there’s a temporary workaround by using the terminal (or an Automator/Siri shortcuts):
https://www.totalphase.com/support/articles/200349376-Multiple-Application-Instances-on-Mac-OS-X
Haven’t tried but maybe would help to avoid having to duplicate massive apps.