I want to be able to have my customers view the project board and contribute as a team member so that they can also be assigned tasks to track. Is this possible? Can this be done so that they do not see other projects that are not relevant to them?
Short answer: mostly yes.
You'll need to spend some quality time setting up (and maintaining) permission schemes and/or project roles to support this. Permission schemes and roles control who can see what, and also what actions they are allowed to perform. More here:
To help further, you'd need to clarify if your projects are next-gen or classic (or both). There are different approaches, based on the type of project(s).
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