Which is fully appropriate where it exists.
I would be 100% against the US having a 'Constitutional Monarch' but I'm 100% in support of the UK Constitutional Monarchy, given that it has come from their long established culture, nearly a 1000-year-old 'contiguous-ish' institution.
FYI in 1258 the Monarch signed documents which required him to 'Confer with Parliament' when changing rates of taxation. That's only 40 years past Magna Carta, and the first reference to 'Parliament'.
The romantic in me likes to believe the Queen would step in if the British parliament tried passing some truly terrible bill. Basically acting as a last stop gap of human and British sensibility. Though with Queen Elizabeth II gone I'd have less trust in the judgement of a monarch.
Part of me does wonder if US politics would've been much different with a ceremonial figurehead. And that'd be a fun alt-history where a great-great-grandchild of George Washington is the ceremonial head of the US government and has to deal with intrigues of Washington politics while just wanting to live quietly on the ancestral Virginian home.
There is no clear '4 years to election' as they have in the US.
In my home country, Canada, it gets dicey as we wonder sometimes just what the 'Governor General' (Queen's rep in Canada) will do.
I don't think the Queen is going to be interjecting on any 'legislation' unless there is something fundamentally unconstitutional about how it was passed; but there's definitely some question marks about 'how and when government falls and is formed' - and especially, how 'minority governments' are formed. If there's no obvious winner, then minority situations form, and it can get weird.
That's still a thing.
I suggest the US would have been a better country were the American revolution to not have happened. Sounds totally crazy, but true. I think the US would have healthcare, be a bit more socially minded, slavery would have ended a lot sooner, and the US still have all of the 'good parts' (except a cool national anthem).
There has been a lot of speculation over the years about whether Charles might be a more activist monarch, but I’ll be really surprised if he actually tries to exercise any of his theoretical powers. He might be a bit more outspoken in public, and do a lot more lobbying in private, at most.
Otherwise, we might need a 'Supreme Parliamentary Council' to basically enact those duties, and if any members of Parliament didn't agree on the outcome, they'd take it to the Supreme Court who would rule on it kind of thing. Something that would only happen 'once in a century'.
Where there are Presidents, it's generally straight forward: the Dude with the most votes (of whatever type) is the Dude and that's it. There can be voting shenanigans but generally not outcome shenanigans.
I'm fine the way it is in the UK and Canada, I wouldn't change a thing.
If we want reforms, we can do that at more operational levels, aka 'governance by blockchain' to put it in 2019 Valley terms.