[Splatoon 3]
It appears Nintendo will add the ability to create Plaza posts without a Facebook or Twitter account sometime in the future.
A server-side switch for this feature was added in 4.1.0. Tutorial text was also changed to remove references to "social media".
There wasn’t a Mastadon post yet, so a twitter frontend is the next best thing.
I never had the chance to experience Miiverse. I’m looking forward to using this!