[Pseudoscience-is-malarkey (OP)]

How would most Brits react if King Charles summoned a press conference to announce that he has begun taking GnRH modulators, estrogens, antiandrogens, and progestogens to transition into a woman and become Queen Charles?

[Petrochemicals]

sh1t a brick probably!

[Eternal Student]

Hi.

I really don't know but overall the question could have been stopped after the first half...

How would most Brits react if King Charles summoned a press conference?

     Unless it was Christmas, they may not even switch on the TV set to listen.   Are you from the U.S. by any chance, you do seem to use some US spellings.   It's been a few years since the King really acted like a head of state for the United Kingdom.   Personally I'm reasonably happy with the Royal Family but there's a good number of Brits who are not and are described as "anti-Royalists".  Don't get me wrong, they aren't going to put the Royal Family on a Guillotine but they believe there's no need to support the Royal Family in the style that we currently do when tax-payers money can be spent on other things.

....to announce that he has begun taking GnRH modulators, estrogens, antiandrogens, and progestogens so he can become a woman and become Queen Charles?

    To be honest, the first thing to cross my mind would be that this was a bit of an over-inflated PR exercise.   I mean it would do no harm to have the Royal family seen to be involved in current issues being explored in society.   There would no doubt be books written and films made about their struggle with gender identity but they were never allowed to express themselves because of their duties and role in the Royal Family.   I can see the end scene - a real tearjerker.... they heroically stand up in front of the whole nation and say "I am what I am"   (...so you just know that the later stage versions will use the Gloria Gaynor song of that name but you're going to have wait for that).
   Would it cause the majority of U.K. citizens to recoil in horror?  I wouldn't have thought so.  Get a good ghostwriter for the book and some good actors and screenwriters for the film version and it will probably put Britain back on the maps again, an international "tour de force".

Best Wishes.

[Zer0]

Long Live the Queen!

[Bored chemist]

Tens of thousands of people queued to walk past the Queen's coffin.
In a city of ten million that means well over 99% didn't bother.

I think that's' roughly the same reaction you would get to the King deciding to transition.
I think 99% of the population would realise it really didn't matter.

[alancalverd]

We've had lots of kings and a few queens.What matters is that the head of state is not an elected  moron or a hereditary scumbag, and they have generally behaved themselves since Cromwell showed what happens if they don't.

[alancalverd]

Tens of thousands of people queued to walk past the Queen's coffin.
In a city of ten million that means well over 99% didn't bother.

Those that did queued for up to 2 days to do so, and the show was time limited: there simply wasn't any chance of the other 99% getting in. The procession from Balmoral to London and the funeral were major television events watched by almost everyone who wasn't at the roadside.

[Bored chemist]

The procession from Balmoral to London and the funeral were major television events watched by almost everyone who wasn't at the roadside.

Even the BBC says it only got 28 million viewers.
https://www.bbc.co.uk/news/entertainment-arts-62966616

[alancalverd]

they aren't going to put the Royal Family on a Guillotine but they believe there's no need to support the Royal Family in the style that we currently do when tax-payers money can be spent on other things.

Currently, about £2 per capita per annum. The alternative? Think "President Truss".

[Eternal Student]

Hi.

Currently, about £2 per capita per annum

   As I mentioned I'm sufficiently in support of the Royal Family that I don't mind paying that much.
   Just to be fair, you could have phrased it differently,  it's over £ 100 million per year   AND some property.  The land and property assests (like Buckingham palace) used to keep the Queen right at the top of the list of wealthy people in Britain a few years ago (I don't read all the latest magazines these days).  Presumably, the anti-Royalists would intend to sell or re-purpose the property.

Best Wishes.

[alancalverd]

Any countable sum of money is better than an elected president. The only thing worse would be an unelected president, like Thatcher, Blair, Johnson, Truss.... but at least they had to get royal assent to any major stupidity.

[alancalverd]

The procession from Balmoral to London and the funeral were major television events watched by almost everyone who wasn't at the roadside.

Even the BBC says it only got 28 million viewers.
https://www.bbc.co.uk/news/entertainment-arts-62966616

Not a bad audience for watching people sing songs around a corpse in a box. Beats the Cup Final, where the outcome wasn't known in advance.

[alancalverd]

Presumably, the anti-Royalists would intend to sell or re-purpose the property.

You could sell it to, er, another farmer, perhaps. Not sure repurposing would be that good an idea. IIRC the King owns a couple of nice cars, Sandringham and Balmoral - draughty headquarters of large farming estates.  Almost everything else belongs to the Crown (a peculiarly British concept, but basically the taxpayer). So the only question is whether the royal family are good landlords. Have their tenants complained?

[Bored chemist]

Not a bad audience for watching people sing songs around a corpse in a box. Beats the Cup Final, where the outcome wasn't known in advance.

So, it's marginally more important than finding out which of two bunches of people is better at kicking a ball around a field.

Sounds about right.

[alancalverd]

Objectively, a funeral is about the least important event in anyone's life, whether they are centerstage or in the audience. Little point in betting on the outcome or wondering if someone is going to demonstrate exceptional skill and strength. Not even a fond memory or aspiration "I wish I could do that".  So if the least important point of a queen's existence gets a bigger audience than the finale of a 9 month knockout contest between some of the world's most talented athletes, I think we can deduce that said queen was a bit popular when she was alive.

[Bored chemist]

Objectively, a funeral is about the least important event in anyone's life,

It's not in their life.
Funerals are for other people. In that context they may be very important.

Objectively, watching people run round a field is unimportant.
It may be entertaining, but other forms of entertainment are available (Football has the advantage,as a participant, of being quite cheap.)

As you point out, the same is true of the Queen.

Currently, about £2 per capita per annum.

And I agree that's a small price to pay to avoid a President Truss (or President Blair or even President Corbyn).

But I can't help thinking there's a better way.
The UK's Eurovision entry will be decided in a more democratic system than our current laws.
Who knows; a real democracy might even undo Brexit.

https://www.statista.com/statistics/987347/brexit-opinion-poll/

A system with a monarch who has power but only if they don't wield it (ask Cromwell), is absurd.
It does mean we have someone quintessentially nice to send to state occasions.