What feature do you want to see added?

I saw changes in the latest PR #2806 , will AuthMe drop support for versions older than 1.16-?

Maybe we could use libby to download libraries dynamically instead of using SpigotLibraryLoader, also can keep compatibility to older versions.

Are there any alternatives?

Already described above

Anything else?

No response

The plan is to drop pre 1.16 support for the final 5.6.0 release, beta3 will sill support 1.8-1.15

we need old versions

The plan is to drop pre 1.16 support for the final 5.6.0 release, beta3 will sill support 1.8-1.15

Furthermore, that library doesn't share the same location with Spigot's system (ref). This means dependencies would be downloaded although they are already downloaded and available for other plugins or even Spigot itself.