Do you have the source of the library module that generates the AAR package?
If yes, I could try and see if I can recompile the library with the "coreLibraryDesugaringEnabled" set to true.
Oops: just saw that was the link Don already posted.
See here:
https://developer.android.google.cn/studio/releases?hl=en#4-0-0-desugar
The docs talk about the app's build gradle file. I am not sure if it can be applied to the library's build grade file.
Otherwise,
Don't know if this can be of any help. It talks about a standalone tool.
https://www.reddit.com/r/androiddev/comments/m4cryu/generate_a_desugared_jar_using_a_standalone/
I wished I could be of further help.
Perhaps Erel has some more information and if it can be resolved.