I thought that if I entered a Fediverse address here, like '@FrankM@nrw.social,' it would follow that user, and their posts would then appear in the corresponding category.
But that's not happening. There's also no meaningful error message. The actor you see in the image probably appears because I entered an incorrect address.
Does this feature need to be enabled on the Fediverse instance 'nrw.social'?
Who can help?
Yeah, as mentioned - Lemmy is often quite bad at sending the 'Accept' back for a Follow. It's particularly the case if the instance hasn't heard of you before, because in the process of fetching your user and instance details, it 'forgets' about the Accept. Within Lemmy, everyone's sort of got into the habit of 'Subscribe / Unsubscribe / Subscribe'. (where the first 'subscribe' lets them get your details, and the second one actually gets an 'Accept' back.)
PieFed is more reliable at sending 'Accept' back, so it's maybe useful to check your logic from this end with a community from there, e.g. https://piefed.social/c/antisocialmedia