It depends on the project 

 I volunteered as a PM to get started on my first crypto project. The project lead wrote a post-mortem about a failed product launch. I replied to him describing how a PM could help the next launch attempt succeed and joined the project based on a subsequent conversation.

I do find it difficult to be accepted as a PM in the decentralized world, although as the year have passed that resistance seems to be diminishing. Rather than "management"I tend to think of the work as "coordinatation", which tends to be perceived as less centralized and heavy handed.

One tactical step you could take is to create a GitHub project board from an existing project and try and do some initial organization of current issues. If you're not a contributor to the repo, try forking it and creating the board in your fork.

Hope that helps a little...