Thank you very much. At first, I thought there was again a misunderstanding because I had already tried this without success. But then, I realized that my mistake was that I had already done something using hidutil shell command. That was in conflict with BTT.
So once I cleaned everything nicely, your proposed solution works perfectly.
I didn't want to create a new subject not to pollute the forum too much...
The shortcut works like a charm. I enabled the "Allow to trigger again..." option. But it's probably not what I thought it was.
Now that my Cmd key located at the right of the spacebar is triggering a forward delete, I expected to maintain the right Cmd key down to forward delete continuously several characters. But it doesn't work. I have to lift up the key, then press it down again, etc. to forward delete multiple characters. Is this normal?