From my perspective the spam wave seems to have subsided, or maybe this post brings it in again... What I did:

On Pleroma put the discord invite url and the hashtag in MRF as blocks. On Friendica I don't have MRF, so I unsubscribed from guppe groups. That seems enough, I haven't had to block any domains yet, may do so later if needed.

The hashtag should probably not be blocked forever, as it is the Japanese name of a legitimate business which may be the target not the source of the impersonation/defamation attack, as is the discord. But since I have no Japanese contacts, that's ok for now.

I always have private messages blocked from people I don't follow, and I recently started hiding followers/followed accounts, which I think also helps a bit to limit such waves.