Does the sterile cockpit rule mean flight attendants could not inform the pilots if a passenger is in the lavatory while on final? Context:
I've seen this interesting question just the other day, asking what would pilots do after receiving this information while on final:
either go around or continue with the landing. 

However many others mentioned the Sterile cockpit rule under 10,000ft. Meaning that they could not discuss this issue.
So what would this mean exactly? The flight attendants could inform the pilots but they can’t respond?? Or the FA’s just can’t/won’t inform the pilots about the situation at all?
"Sterile Cockpit" refers to the concept that pilots should not discuss anything not related to the flight during certain phases of flight (often defined as below FL100).

A passenger occupying the lavatory while the flight is on approach and passengers are supposed to be in their seats definitely does have an impact on the flight, so it does not fall under the "sterile cockpit"rule.