How to directly convert .sb3 files to .mp4 format.
With previous versions of Scratch, it was possible to export SB3 files (Scratch 3.0 Projects) to Shockwave Flash format, which could then be easily converted to MP4 format.
First, you might have to import the SB3 file to an older version of Scratch. Then, you export it to SWF format, and use one of the numerous multimedia conversion utilities to obtain an MP4 video.
It's quite the workaround, but it might work as an SB3 to MP4 conversion.
A programming language used to create interactive stories