@Dr_HansD : It seems I made an error by just referencing to the site where to find the list of licenses, and not checking myself if it is included. In the list of software benefits for Action Pack, I did not find Project Online, only Project Professional 2019.
Did you maybe look in the list for Silver/Gold Partners and not the list for Action Pack?
@Dr_HansD : You can access the list of licenses included in the benefits here: Internal Use Rights cloud and software benefit (microsoft.com)
Download and activation happens in the Partner Center: Manage Microsoft Partner Network benefits - Partner Center | Microsoft Docs
Many thanks for that, it shows up that we have project online E3 plan available, but it does not allows us to download it, the only 2 options are Office and Skype.
I guess "the only 2 options are Office and Skype" probably refers to the user experience in office.com - so do you see the benefit in Partner Center and can you activate it? IF you have activated this, can you see the licenses are available in the M365 Admin Center (admin.microsoft.com)? Did you assign the user that wants to use Project the Project license?