It's called Lèse-majesté (in English, that is). It is still actively persecuted in Spain [0], forcing Belgium to reinterpret its current laws in order not to extradite a rap singer.

[0]: https://en.wikipedia.org/wiki/L%C3%A8se-majest%C3%A9#Spain

I'm neither a legal expert nor a British citizen, so I may be wrong; but pacific protesters holding anti-monarchy banners were arrested by the Metropolitan police before the coronation of the new king, although they were neither violent nor doing any kind of obstruction.

Holding a sign in the street can land you in jail in the UK, in 2023.

https://www.theguardian.com/uk-news/2023/may/09/tory-mps-con...

https://www.bigissue.com/news/activism/public-order-bill-exp...