I would expect some kind of filter to exists on website or in console.
Setup a .NET Core project in the version you want. I keep 1.1 and 2.0 projects around for futzing with this. Then try and add the nuget to the project.
For instance, ASPOSE will NOT add to a 1.1 project, but will add to a 2.0 project.
Easiest route in the short term until they fix this somehow.
Obviously this is no guarantee it still works but gives you a good idea if its api compat.