Anybody know how to convert an .sb3 file to an .sb2 one?

Impossible, Scratch 3 added stuff that Scratch 2 doesn't have. S2 isn't forwards compatible, and won't receive updates anyway.

Change .sb3 to .sb2 or use .sb dowloader.

MintSafe399386_1 wrote:

(#2)
Impossible, Scratch 3 added stuff that Scratch 2 doesn't have. S2 isn't forwards compatible, and won't receive updates anyway.

Someone already did it. (although I don't think it converts 3.0 features into stuff compatible with 2.0)