SP struggles

Hello all,

Great community, of which I kindly want to use your expertise :)

We are an average organization with an O365 SharePoint online environment. The current environment is a mess with rights and authorizations. At the moment we are also setting up Role Based Access. The setup is as follows:

Default configuration

For the different departments we have a standard team site with the underlying SharePoint site.

Based on RBAC, the correct authorizations are automatically assigned.

For employees, sharing files in teams and SharePoint has been disabled (so sharing with users who do not have authorizations for the relevant Teams or SharePoint site is not possible.) This has been done deliberately in order to comply with information security standards.

Problem

There are situations in which employees from other departments (temporarily) have to work together with employees from the department. In that case, they also have to work together on documents. Now my question is, how can we ensure that people can work together without the employee from the other department getting rights to the (full) Teams and/or SharePoint site.

If anyone can help me on my way that would be great.

Thanks in advance,

Peter