How to resave all my nodes In D7, it was easy with the VBO module..
But how to do it with D8? (Preferably using a view to select the nodes to resave)

In many places I saw that a small part of the VBO module is now included in the D8 core but I can't figure out how to use it (assuming a simple save should be feasible)
What you are asking for is included in core Views, unless I am mistaken.
In a new Content view you will be able to add a "Content: Node operations bulk form" field and that offers you an option for "Save content".



You could even use the default "Content" view...



that already offers that option out of the box: