Are general niches harmful to my backlink profile?

tnx for all

Are you asking if general niche websites are damaging your niche-specific website? Up to a degree, of course not. It wouldn't hurt getting a few niche related backlinks to have a more natural looking backlink profile, but remember that most big news outlets are general websites and a link from them would never hurt.

It depends. If you're just blasting links randomly then yes.

Porn, Hack, Poker, Pills, illegal stuffs.

(exept you are in these niches - but some will deindext from Google.. so)

Links from niche relevant blogs do work better, but that doesn't make a general niche one kind of harmful or spammy,
If you aim for some links from decent websites, do pass link juice and help to rank for sure,

The difference is just like the recommendation of a lawyer for some doctor versus a doctor for another doctor,
Both do count, but doctor recommendation would simply matter more