"That is what they are supporting."
Translation:Das ist, was sie fördern.
der, die, das can mean either "this" or "that".
dieser, diese, dies(es) generally only mean "this".
So saying that there is no difference between "this" and "that" in German is not completely accurate; it's specifically the der, die, das which do not make a strong distinction and can be used for either.
(There is also jener, jene, jenes which is specifically for "that", but essentially nobody uses those any more. I don't think they're accepted in the course. They're probably about as common in German as "yon" is in English: nobody I know would say "yon book".)
"Das ist, was sie fördern."
"Das ist, was sie unterstützen."
"Das ist es, was sie fördern."
"Das ist es, was sie unterstützen."
Simplifying the translation to "Sie förden es" or "Sie unterstützen es" is not accepted, and shouldn't be. Duolingo wants faithful translations, not simplifications.