Transparency on eevee

Hello

transparency on eevee is not working here.
and when it is at zero the object turns black
follow image

thank you

imagen You have to set the Blend mode to Alpha Blend.

Thank you for your help

tell me one thing :

is it normal for the viewport, with eevee on, to get heavier when the file gets big?

It will depend of your hardware, but it’s normal that the viewport gets heavier with more objects.