In the past years, Developing Mountainbiking in Scotland (DMBinS) researched, developed and run a program which offers group mountain bike rides to people with a mental health condition, like anxiety or depression.
Read more about the program in this article.
Key elements are the physical activity in a natural environment, the connection and support in a group, and the experience of challenge as well as fun. Participants are also invited to dive into mindfulness techniques like meditation or grounding, to enjoy stillness in nature, and to share their experiences in the group.
I highly recommend watching the beautiful 11 minute film Recovery about the program.
Have a look at the FAQ section for practical information.
Below are more resources worth a look. Enjoy!