best response confirmed by Juan Carlos González Martín (MVP)
Solution

@Michele Casazza It is good you found the information already on desktop application requirements.

However, I'd like to point out also that Office Online allows co-authoring. So you can co-author many documents without the need for Office Proplus. However, Online doesn't come en par with desktop application functionalities and there are limits in documents (especially Excel) that is supported. 

 

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