When I go to Site Administration -> Plugins -> Install Plugins; I drag the Zip file into the choose a file box, then select Themes from the plug in type. After clicking on Install plugin from the ZIP file, I get that error message.
Our version is 3.9.2 (Build 20200914).
I've ran the support tool and the code is: b57fc1dc-2037-b3b4-aad9-9b5928be6c8b
Let me know if you need more information from me.
Appreciate your help here