Unauthorized Access to My Steam Account and Theft of CS2 Inventory

My Steam account was accessed from Russia without my permission, and I received no notification about the login. Despite having two-factor authentication enabled, it seems like it was bypassed, and my entire CS2 inventory was traded to an anonymous user without any alerts. I have never engaged with gambling, trading sites, or anything similar—I am strictly against such activities. Steam Support has been unhelpful in addressing this issue. What steps should I take to resolve this? I need guidance on how to recover my account and items.