Plex and Plex Media Server cannot be opened

I’ve downloaded and installed Plex (1.2.0) and Plex Media Server (1.16.5) on my Mac. However each time I try to open them I receive the error:

“Plex” can’t be opened because Apple cannot check it for malicious software.
This software needs to be updated. Contact the developer for more information.

I’m running MacOS Catalina, 10.15 Beta (19A546d)

Has anyone else ran into this issue? How can I resolve this or download the previous versions of Plex and Plex Media Server