Filtering out based on substrings

Dear all,

Assume FILES is a variable that contains a list of files with their
path.

Is there a way to filter-out just the files whose path contains
/bytecode/, for isntance?

My naïve attempts to call filter-out on $(FILES) with patterns like
%/bytecode/% failed and made me realise it's not possible to have more
than one % in a patternn, if I understand things correctly.

I also considered doing the filtering in two steps, but even that would
not work because the pattern would have to appear either at the
beginning or at the end of the string which is precisely not the case.

Any hint warmly welcome.

Many thanks in advance,

Sébastien.