applicability in or to

Solution 1:

Apply and applicable take a complement (an essential part of their meaning) with "to".

If you say applicable to real-world environments, you are stating that the real-world environments are (among) the things that it applies to.

"In" does not introduce a complement of apply or applicable, so it must be an adjunct with its normal meaning. So applicable in real-world environments must be talking about the environment within which it applies, not the things that it applies to (which are understood).

Whether there is a substantive difference in meaning depends on factors outside the sentence.