...if I understand well, Adobe Air is no more available.
Adobe have passed the development and support of AIR to Harman but AIR is still an active and valid platform.
Unfortunately, now that Adobe have passed AIR to Harman, they have removed their regular Adobe AIR download page (redirecting users to the Harman site) and, at the moment, Harman provide only an AIR SDK (a Software Development Kit for developers) but not an AIR runtime (for AIR application end users).
Installing an AIR SDK will not allow you to run the JuiceboxBuilder installer. An AIR runtime is required.
This makes life a little difficult during this transitional period.
However, it is still possible to download the most recent AIR v32.0.0.125 runtime directly from Adobe via the links below:
Mac: https://download.macromedia.com/air/mac … obeAIR.dmg
Windows: https://download.macromedia.com/air/win … taller.zip
Once you have downloaded and installed AIR from the links above, you should be able to pick up the Installing JuiceboxBuilder instructions at Step #2.
At the moment, although Harman provide only an AIR SDK, they hope to provide an AIR runtime very soon.
According to a comment (from five days ago) on this web page, Andrew Frost (Harman's Software Engineering Manager) says:
... we are looking to provide a shared runtime still, for end users to download.
We should have things resolved and uploaded within the next two weeks I believe.
In the meantime, until the Harman AIR runtime is made available, the most recent Adobe AIR runtime can be downloaded from the links above (or from software download sites such as Softpedia). However, if you download Adobe AIR from any website other than Adobe's own, then please do so at your own risk.
Incidentally, the most recent Adobe AIR beta runtimes (v32.0.0.144) can still be downloaded from the Adobe Labs page here.
I have notified the Juicebox developers of Adobe's website change and our installation instructions should be updated in our next website refresh.
Another question: will Juicebok-Pro work on MacOS Big Sur?
Yes, but you'll need to implement the fix (first required for MacOS Catalina) noted here.
I hope this helps.