does my microwave oven have acceptable leakage?
Routers typically simplify (to the point of lying) in their power level displays:

Your router doesn't really care about the power level of your reception; what matters to it is that it's not far too weak or far too strong (but as you know from operating devices from orders of magnitudes of different distances from the router, that's not often a problem), and how the power relationship of desired signal to (noise plus interference) is.

So, they display some number that is often something like "if there was true gaussian, stationary, white noise, at powers like we'd get for a fixed noise figure, we'd have this much signal energy." Note that this is implemented differently by different WiFi chipset vendors, is partially specified, is mangled by driver and UI software.

Problem is that the things that are hard on the reception quality are exactly these interferences that are correlated to the signal, that are bursty and high-powered, that take the same statistical properties as subcarriers. So, not really closely linked to received signal power.

So, your router's power display tries to be helpful at displaying how good reception is. It really doesn't try to be an RF power analyzer.

That means I wouldn't quite lose my head over your microwave oven's leakage just based on your router's quality assessment.

If you really had 10W (more like at most 6W, considering efficiencies and internal absorption) escaping your microwave oven, you could even just get e.g. fridge-cold margarine and smear all gaps around the door and check whether that margarine gets liquid. (Be careful – don't smear the vents of the thing; the warm air that comes from cooling the power components inside needs to go somewhere, and that would a) raise a false alarm and b) smell bad from the inside after a couple of weeks).