Thank you to @DaveR and @slbaumgartner
Thanks, I just a had “a moment”, a blank moment… Duh !!!..
…for those who might read this post, and need assistance :
To hide geometry on “Layer 0” use those 2 steps :
A) make another layer than “Layer 0” Active --> use the radio button/check mark on the left of any other layer (create one if necessary) and check it
B) then you can hide “Layer 0” --> by checking the radio button/check mark on its right.
==> do not forget to switch back to making “Layer 0” active/reverse those steps, as draying in this mode might create issues with your model.