The upcoming MacOS 10.15 blocks the install of GP 3.5 as it sees it from an “unidentified developer” - the MacOS 10.14 approach of using the Security prefs pane to bypass and “Open Anyway” is no longer available in 10.15. Just a heads up, as we are in a Public Beta situation for 10.15. The development team will need to research the new MacOS Gatekeeper requirements for app scanning on install and launch.
UPDATE - ctrl click on the installer will still let you install with admin privileges.