Is it possible, to pass binary data to XSLT?

Depends on your processor, the commercial editions of Saxon Java (and
C?) do support
https://www.saxonica.com/documentation12/index.html#!functions/expath-binary
and
https://www.saxonica.com/documentation12/index.html#!functions/expath-file

So there you have functions like
https://www.saxonica.com/documentation12/index.html#!functions/expath-file/re
ad-binary