Thanks for explaining that. I know your Home Secretary is a Muslim woman...and she's responsible for your borders and I think the police. So "shadow" Home Secretary means what exactly? Would he be a candidate for Home Secretary in the future?
I'll try and explain. In a General Election (when UK citizens vote for candidates to become Members of Parliament), voters in each constituency (electoral district) vote for which candidate they wish to represent them as their Member of Parliament. The candidate with the most votes in each constituency becomes an MP. In the last General Election, Labour had the most MPs elected, so we have a Labour Government. The MPs from the other parties, and the independent MPs (Conservatives, Liberal Democrats, Reform UK, the Green Party, etc.) are the Opposition.
Now, when all the votes are in and counted, the political party with the most MPs forms the Government, and the MPs from the other parties form the Opposition. Then, the Prime Minister chooses from his Government people to bear particular office, for example, Home Secretary, Foreign Secretary, Chancellor of the Exchequer). The Opposition leader likewise chooses from its number their equivalents, such as Shadow Home Secretary, Shadow Foreign Secretary, Shadow Chancellor of the Exchequer.) These "Opposition shadows" are there to hold their Government equivalents to account, and to say what their party would do in a given situation if they were in Government.
You ask if the current Shadow Home Secretary would be a candidate for Home Secretary in the future. That would depend on many things. First, his party would have to be in Government, not Opposition. Second, he himself would have to have been elected again as the MP for his constituency. Thirdly, the Prime Minister of the day would have to choose him as Home Secretary.
I hope that helps. It can be difficult to understand the politics of another country - I don't really understand the voting system in the United States, with its Electoral College, and so on.