There has to be some third-party service to this

For .sb2 to .sb1 files you can use the “Retro Converter” made by blob8108.
For .sb3 to .sb2 you can use Rex's sb3tosb2 which you can find on this topic or you can open Scratch 2 on your browser using s2online, which can also convert from 3.0 projects to 2.0.

Hope this helped!

What about .sb

codepig8211 wrote:

What about .sb

the post above yours has already answered the question