@vicgrinberg
If you mean the server admins they list an account and a contact email here:https://mastodon.social/about
Since dev happens on github I expect that is the most direct way to highlight your complaint to devs, but I've also seen people speaking directly to some of the more famous devs on masto, like Eugen. Not sure how well that works in practice.
(my wife tends to just make a new girhub account when she forgets the details to the old one)
@vicgrinberg
(I wondered if you meant you didn't like the instance running beta features)
I couldn't find any other "official" channel, and since open source is at its core a developer philosophy I'm not surprised: open source projects tend to expect a substantial level of familiarity with development practices from those that address them directly.
Usually what exists is github and maybe some social media channel, and it takes a long time until a project develops enough formal structure that it creates some sort of public friendly feedback mechanism.