What project management services exist for the interaction of two companies?

Question

Project management

There are two independent teams and a number of projects. Some of the projects are shared, that is, they are carried out simultaneously by two teams. Some projects are carried out by only one team, and these projects are confidential, that is, the second team should not have access to these projects from the first. What services exist that allow you to implement a management system for similar projects for two teams?

The problem with almost all existing services is that they have a single admin who has access to all service projects. We also need a service in which two independent working groups can be integrated into each other partially, or a service in which the main admin does not have access rights to all projects of the service.

Answer 1

Alternatively, two teams should use the same service, purely for convenience, independently of each other. For those projects where another team is involved, give guest access. At a minimum, Planfix has this, I also met it in others.
"the main admin does not have access rights to all projects of the service." - the requirement is very complex in terms of logic :)