https://github.com/ruby/rbs
is the "officially supported" one. It's terrible, as is Sorbet. No offense to anyone involved with either of the projects, they just miss the mark in pretty fundamental ways.
Type definitions were introduced in Ruby 3. I personally think they are terrible --- primarily because they exist in sibling type files. They are arduous to write, don't have great tooling support, and don't feel like a part of the language at all.
Official way? I thought there is none.
As long as there is no support for gradual typing in the core language it will never be used outside of niche programming.
And then I have a hard time imagining that Rails would use it anyway. Unless the performance boost would be tremendous.