You can access feddit.de's communities and discussions from lemmy.ml for example, no need to make an account on feddit.de or visit feddit.de at all. Theoretically you could also access feddit.de forums from hexbear if/when hexbear enabled this feature (called federation). But feddit.de has added hexbear.net to the list of banned instances preemptively, just in case, so they can't see us and you can't post there. I think this also means feddit.de users will not see any posts by any hexbear account, even if they're part of the same discussion thread on lemmy.ml.

So, you might reply to some German's braindead post on !worldnews@lemmy.ml, but they won't see it or know you replied at all.