The location of the dark mode option is inconvenient for many of my members. Can it be integrated with the "user" display in the header ?

Most likely yes. I wouldn’t mind having a go at it to make a small hook and share it here.

There you go: https://invision-market.com/apps/members/lightdark-theme-toggle-100-r128/

Fabulous ! Thank you . Installed and works as expected.