In Debian 11 Bullseye (current testing) and Sid, scilab-full-bin is not available for armhf and i386, but in Debian 10 Buster is avaible.

Perhaps this is due to the limited number of architectures supported by libjogl2-java: bug #926069 relate to #887140

But upstream, a downloadable package is available for i386, view  https://www.scilab.org/download/6.1.0
This makes me think that it might be possible to package it for the missing architectures, even if it is by disabling some feature (libjogl2-java support?) when compiling.

Thanks!