Well, I finally understood.
When I start Fallout 4, I go into workshop mode, I try to put the yellow mark, but it can't be created
So, I create any different object on another site (letter
B for example)
Now I can create the yellow mark
but I can't target the yellow mark or move it with Place Everywhere's controls. But I have read
@Strong Swanson 's notes on known issues,
I have left / entered the workshop mode and now it works
I can use now Place Everywhere's controls to nudge them into the correct place.
Another little problem, I can't see the name of the painted numbers
It seems that it is a known problem, but not being able to create the marks or numbers until I have put another object has confused me for a while.. It also happens that I can move the panel and the letter B all together, but not the marks, I guess everything comes from the same..
I'm not trying to make a bug report, I'm just testing the translation.