Note that developers starting the collaboration session (host) do not have this limitation. It is specific to participants joining a session.

Currently the developer that started the collaboration session (host) is the only one that can trigger a build or start a debugging session. While it provides the owner a high degree of control, the downside of this approach is that guests will be unable to start a build or debug while the owner is away temporarily. We could allow guests to run a build or start a debugging session to solve this challenge.