What social media platforms do natives use? – and some other random questions

Title. Could you share what platforms you mainly browse, and if you think they are widely used or only a niche platform? Here I mainly mean public platforms (so not LINE), and that they have a nice amount of native speakers (does not need to be fully Japanese – partially is totally fine) and, hopefully, the users are generally friendly.

I know what 野獣先輩 means, if that matters.

Also, could someone explain what kind of place is Niconico Douga? The app design is shockingly old-schooled but still many masterpieces come from here.

Thank you in advance!