Hi, @Roger Roger
Looks like the issue is more related to Microsoft Project. Please kindly understand that the Exchange Online tag here we mainly focus on general issues about Exchange and mail flow.
I noticed that you also posted the same question here, you can wait for a more professional answer. You don't have permission to access items on this site | Microsoft Community Hub
Based on my personal search, these articles may be helpful.
Change your default PWA site - Microsoft Support
Cannot Access Newly Purchased Project Online with License - Microsoft 365 | Microsoft Learn
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