While the U.S. has legal tools to limit business activities of foreign-owned online services and apps, it can't currently block direct access to them. First Amendment concerns aside, the technical means to control digital traffic into and out of the country are legally beyond government control under an arrangement finalized in 2016 with ICANN after nearly two decades of discussion and debate.
ICANN is a Los Angeles-based nonprofit structured to be independent of any single government. It along with 11 other organizations collectively oversees the internet's backbone domain name system that connects users and web addresses. In relinquishing its authority to an independent entity the U.S. hoped to encourage a free, open internet, but that hasn't stopped efforts by China and other regimes to throttle their own citizens' access to some U.S. websites and apps.