In my opinion, being a project manager in a Matrix organization is harder.
The PM has to deal with two bosses and constantly negotiate with functional managers for resources. This makes decision-making slow and creates conflicts over priorities.
In a Project-based organization, the PM has more control, and the team reports directly to them, so coordination is easier. Because of the shared authority and negotiation issues, the Matrix structure feels more stressful and complicated for a project manager.

I think that it would be more difficult to work as a project manager in a matrix organization. In a project-based organization, project managers automatically hold authority over their project team, but in a matrix organization, that authority becomes shared. Project managers may have to negotiate with functional managers for a staff member’s time, which can make resource planning more complex. As a result, they may struggle to assemble the exact team they want if functional managers decide to withhold key personnel for departmental work. Competition between department managers and project managers can create tension, especially when expectations aren’t clearly defined. If communication isn’t strong, conflicts between project managers and department managers can escalate, possibly leading to frustration across the teams. These unresolved conflicts can create a toxic work environment over time, making it essential for matrix organizations to prioritize collaboration. Overall, a project-based organization would be easier for a project manager because resource allocation is more straightforward.