Recently, I've read an article on DefenceOne - an interview with James Jeffrey, US ambassador on Syria.
“We were always playing shell games to not make clear to our leadership how many troops we had there,” Jeffrey said in an interview. The actual number of troops in northeast Syria is “a lot more than” the roughly two hundred troops Trump initially agreed to leave there in 2019.
Is there any legal consequences for misleading president with false repots, or it is allowed?
There isn't an answer that is so general.
Certain kinds of false official reports are prohibited in particular contexts, but there is not a general rule that makes it illegal or a crime to mislead a President of the United States (that's what politicians and lobbyists do).
In the context of the quote it doesn't look like any false statements of fact were made. Instead, it looks like it was a question of how data was classified and presented that made it difficult to determine the most salient facts without further direct questioning which lazy supervisors don't do.
Lying to a superior officer may represent a failure to follow orders and so is punishable in a military court. However, lying is endemic in the military, if reports are to be believed. There is a culture of deception at all levels of the US military.
Lying in a non-military role is normally grounds for disciplinary action, that could lead to being fired. But there are no particular laws for Ambassadors, that don't also apply to interactions between (for example) the head of sales and the ceo of a company.
