(Branched out as a new discussion)
Hi Ppp76655349,
Yes, as mentioned on this page: Download Creative Cloud apps , Adobe Extendscript Toolkit CC is not compatible with Mac OS 10.11.5 or earlier.
You may have to upgrade your machine to Mac OS Sierra or High Sierra to download and install Adobe Extendscript Toolkit CC. For more details about the system requirements please refer to: All Apps Help | System Requirements | ExtendScript Toolkit CC.
Which version of Creative Cloud desktop app is installed on your machine ? Can you please share a screen shot of the 'Preferences Tab' of the Creative Cloud desktop app with us? See: FAQ: How do I capture and post a screen shot or video?
Awaiting your response.