I taught myself Erlang last year and loved it until I tried to write an application. The OTP documentation, while voluminous, was confusing and seemed to have important omissions, and I found little if any community.
I know there's a lot of power there. Whatsapp was written in OTP and had something like half the world using it with a development team of maybe 12.
I'm glad to hear the community is bigger than what I found. I don't actually remember that search process. What I remember clearest was running into the brick wall of the OTP documentation.
If you'd want to try again, I can recommend "Elixir in Action" [1].
It has a great introduction to the basics of OTP later on in the book. I understood it much better after reading that book that any other materials.
While the book is about Elixir (which is a BEAM language) the underlying OTP principles are the same. The book covers "basic" OTP before moving on to some abstractions that Elixir provides.
I'm not sure on your exact timeline, but the documentation has also seen several upgrades.
For example, see the "telemetry" library, written in Erlang and published to the Hex repository. Its documentation is built using the Elixir-based ex_doc https://hexdocs.pm/telemetry/readme.html
There's a lot of great stuff in the BEAM ecosystem, I would caution on writing it off too fast