ONLYOFFICE accuses "Euro-Office" maker Nextcloud and IONOS of License Violation
(www.onlyoffice.com)
assuming they have full ownership
You are mixing things up, I'm not talking about the project, I was exclusively talking about the code someone had made personally.
Linux for instance can never be made proprietary, because it's impossible to get permission from all developers.
But anyone who has contributed a piece of code, can use that piece in other projects under different licenses. Because they retain copyright to their own code.
So as I stated it is academic to the project, and it's especially academic to a fork of it.