One doesn’t really have a political focus while the other one has at least officially associated itself with such beliefs.
In my experience the admins of lemmy.world are much more aggressive in pushing their politics on their users. I left lemmy.world after they did this: lemmy.world/post/2498330
Also lemmy.world usually has trouble staying functional. Leaving it had other perks. For example, the link above wasn’t working as I was posting this, so here is the feddit.de cache of it: feddit.de/post/2073607?scrollToComments=true