We're still missing the link between a generic warning light and the decision to check the oil pressure. Why did they do this?
Max pressure is controlled by the pressure relief valve, usually integral with the pump, and probably only accessible with the sump off, unless it is around the crank nose like on the diesels. Valve is presumably stuck. Removing it and clearing whatever stuck it may be difficult, depending on how tight it is, but more concerning is what jammed it. Any debris must have come from inside the engine, so careful examination of the tiny speck is necessary. On cold start much of the oil will by-pass the filter to avoid starvation, and often pressure relief valves are before the filter anyway, but such debris should not normally be present.
So what has happened recently? Any operational changes, faults with the engine, etc?