Who said there was? Russian troops as free reign in Syria, not U.S. troops.
There have been U.S. troops in Syria since Obama sent them there in 2015. He even added to the number of troops there in 2016. In 2018, President Trump ordered all 2,000 troops removed from Syria, but top diplomat Jim Jeffrey admitted lying repeatedly to top government officials and the President about the number of troops still there. Biden left them there, claiming they needed to be there to prevent Islamic State resurgence, and it ended up with Iranian-backed rebels taking over the country anyway.