To be fair he isn't legitimate head of state- he lost an election and is officially recognized as a usurper and the US had support of those who actually won.
Even if that were true - I don't know nor care whether it is - what business is it of the US and Trump to mess around in other countries?
Large amounts of people call Joe Biden's election illegitimate. You could even say thats the official position of the current government. Would his kidnapping by a foreign nation be okay with you too?
Soke people argue Trump isn't a legitimate head of state. (One of those people is Trump, since he says he was already the president twice.) Should Xi kidnap him?