different tansparency value when i'm trying to draw a texture

When i select a translucent colour, it change its transparency (no matter the tool i use). I don't think it suppose to work like that. i want to use the value that i pick (not a different one).
I use 2021.2 version.
Here's a video trying tu use the pencil tool: https://youtu.be/TftWcxAmBhg