I know, I know. But after weeks of testing, googling, asking developers and so on, this was the easiest way to make it work. Finally. In my opinion buddypress dev team should remove old tinymce 4.9. Or, at least letting admins use other rich text editors easily. As I wrote this is not only my wish.

Ups, I put the code into functions.php.

But isn’t your approach a security issue? It switch off kses for all fields, right? So isn’t modifying this core file the better choice in this case?