Harman have just released their AIR runtimes (v33.1.1.385).
Here is their download page: https://airsdk.harman.com/runtime
Please read the Known Issues regarding these runtimes (on the download page below the links).
Here are the Known Issues which are relevant to JuiceboxBuilder.
Publisher verification. AIR developers can sign their packages either with a self-signed certificate, or with a certificate issued by one of a number of certificate authorities. With the latter, the AIR installation process would normally show a message confirming the vendor details. Due to an issue with the internal certificates in the AIR runtime, the signing certificate cannot be validated hence all applications will show the "unknown" publisher warning - see image on the right. Please ensure you validate where the application has been downloaded from.
Encrypted Local Store. On MacOS, applications requiring to use the "Encrypted Local Storage" feature of AIR will need to set up a local storage area for this. MacOS requests the user's permission during this process, with the request for a password for the "PrivateEncryptedDatak" keychain password (see image on the right). To proceed, please leave the password blank and click on "Always Allow" - this should only be displayed once.
I have tested the Windows runtime on Windows 10 and, other than being presented with the "unknown" publisher warning, it works fine. (I was able to successfully install and run both JuiceboxBuilder-Lite v1.5.1 and JuiceboxBuilder-Pro v1.5.1.)
Unfortunately, I do not have access to a Mac to test the Mac version.
I hope this helps you to get both AIR and JuiceboxBuilder-Pro up and running on Big Sur.
Please let me know how you get on.
Thank you.