Hi all
​​​​​​Lock ring on non drive side of my bottom bracket (french threaded) is constantly getting little loose.
now I am wondering how tight should it be?

Tight enough not to.

Tight as you can get it with a standard spanner.

clean all exposed threads and use LocTite BLUE on this, tighten as tight as you can with a hook-tip spanner, as others have reco'd.

My guess “no name” parts
tolerances are often... sloppy.
loctite blue but probably will need to pull the cranks to assess the adjustment