I doubt he will ever be king as his dad is destroying England.
The King or Queen of UK has been for centuries a ceremonial leader, not a lawmaker. The Sovereign is forbidden by law from entering the political realm All laws and policies governing the UK are made by Parliament.
If you are referring to immigration, that policy originated with the European Union in Belgium, which UK has formally disaffiliated with since 2020 due to its oppressive restrictions on UK law-making and policy. However, a succession of Prime Ministers and their governments have done little to nothing to stop the illegal migration, instead busying themselves housing and feeding illegals, clearly against the wishes of most of the people.
There is little that the King can do but make suggestions to the Prime Minister at their perfunctory meetings. But the King has no actual legal power over Parliament, which is presently run by the leftist, woke party, Labour.