0% Capacity for People
For people, you can now set a capacity of 0% on the Availability tab. This supports proactive capacity planning at the team level.
For example, create a dummy resource with 0% capacity and add it to a team in the Workload/Resource Overview. Then assign tasks along with their effort to the dummy resource before it's clear which team member will take on the implementation. This makes the planned team load visible without distorting the individual workload of single team members.
Once responsibilities are finalized, the tasks can simply be reassigned to the actual team members.

Combined with the existing ability to set capacities above 100% for generic resources like machines or teams, you now have full flexibility from 0% to any upper limit.
Help article: Define Availability of a Person