bhutan maybe?

I mean i'd imagine there were quite a lot of kings that were much like the modern king of e.g. Norway, where they really don't do much other than PR and rubber stamping decisions.

Any ruler needs support from other powerful people, and since crowns were usually hereditary that means sometimes the new king won't be a miserable sack of shit.
I mean put yourself in the position of some medieval prince whose dad was poisoned by an advisor or something, yeah sure you can live in luxury but it's fucking risky, so if you don't just opt to flee 5 countries over in hope of peace you'd probably try to be as inoffensive as possible and just gently nudge things in a non-shitty direction whenever possible.

So granted, not "good" kings, but considering how many rulers have and continue to be absolutely horrible i'd be pretty happy to live under a king who does nothing..

Maybe Juan Carlos, because he abdicated to transition the government from dictatorship to democracy.