As Prince of Wales, Charles has always paid tax; he has always disclosed the fact that he paid tax on the Duchy of Cornwall's profits (his private income). He also funded charities within his trust.
Paying tax was not required, but he always has done so - since his marriage to Diana - for years and years.
It is old news..
Now, as King, it is not surprising that King Charles discloses more about the taxes he pays on his private earnings from the Duchy of Lancaster.
The earnings and spendings of the Sovereign Grant (which is a minor % of the takings of the vast royal properties which is returned to fund the King's public life and many employees etc. has always been published.
The British Royal Family discloses a lot about it's finances.
It is brilliant that the two trusts, set up hundreds of years ago, provide income to The King and The Prince of Wales, free of political bias. The BRF can show favour to the unpowerful, the unpopular, the environment and those without a voice because they are funded separate to politics.
The British public's taxes do not pay for the private income of The King.
Police protection is provided to all who need it, within the regular budget, including The King. So, taxes contribute to that.