Steps to reproduce:
-------------------------
1. Install hr_timesheet and create a second company (e.g., Company B).
2. Create a global project (no company assigned) with timesheets enabled.
3. Share the project with edit access to a portal user belonging to Company A.4
4. Create a task, switch to Company B, and log a timesheet on the task.
5. Log in as the portal user and try to access the project.

Issue:
-------
An `Access to unauthorized or invalid companies exception` is raised,
preventing the portal user from accessing a project they are legitimately shared on.

Cause:
----------
https://github.com/odoo/odoo/blob/b7b3292b6a46c3dbc17aeee0183df0af318bf810/addons/project/controllers/portal.py#L159-L173 During `_prepare_project_sharing_session_info`, hr_timesheet overrides the company determination logic through `_get_project_sharing_company()`. https://github.com/odoo/odoo/blob/b7b3292b6a46c3dbc17aeee0183df0af318bf810/addons/hr_timesheet/controllers/project.py#L13-L18

For global projects, the company is derived from an existing timesheet if one exists. As a result, creating a timesheet in another company causes that company to be injected into the sharing session as the current company.

Since the portal user does not have access to that company, opening the project triggers an access error.

Solution:
----------
Remove the `_get_project_sharing_company()` override. The base implementation already falls back to the portal user's own company when the project has no company assigned, ensuring the sharing session only contains companies the portal user is allowed to access.
https://github.com/odoo/odoo/blob/b7b3292b6a46c3dbc17aeee0183df0af318bf810/addons/project/controllers/portal.py#L141-L142 
This allows portal users from Company A to continue accessing global projects without errors.

opw-6253960



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Forward-Port-Of: odoo/odoo#276937
Forward-Port-Of: odoo/odoo#272161