I always refer to the lounge guide on the oneworld website
https://www.oneworld.com/airport-lounges
It notes specific exclusions for Qatar Airways Privelege Club, American Airlines AAdvantage and SriLankan Flysmiles members and lists specific exclusions at the particular airport but in general OW Sapphire status gives you access to any OW biz lounge regardless of cabin flown provided you are flying on a OW airline.
In the past I have been denied access to a BA lounge but given access to the OW operating carrier lounge but only because the BA lounge was time specific and closed before my flight departed.
Note if you are travelling on Qatar from T4 you will also have access to the Malaysia Airlines Golden lounge.