Thanks @lpb 
Indeed, since 2025, the concept of Divisions has slightly evolved and this is the new guide: What we learned about Divisions, again (A 2026 guide to the new model)
Your use-case is completely compatible. A project doesnât âbelongâ to a division. The project is simply shared with users who can belong to different divisions. Each of them could see the same data, but limited by the features they are paying for, according to their plan.
Division is now only a concept of seat allocation (licenses), not data separation anymore. Cross Division collaboration is easier than before.
Also, important for you:
In your case, PMO portfolio admin (or editor) can add the Starter Divsion project to the porfolio.
However, the Starter users wonât be able to access the portfolio, as they donât benefit from that feature in their plan.
Also, have in mind that sharing a portfolio is only giving access to the shell (the container), the projects within the portfolio should also be shared to the users (or the teams) who should see them. But there is an option in the portfolio sharing panel to also give access to the project(s), when you invite users to the portfolio (as soon as you are admin a project); if not, you can always invite the users or teams manually on each project concerned.
Hope that was clear,
Let me know if you have more questions 