“A party cannot rely upon an expert’s opinion to establish duty, which is a question of law for the court.” (Thompson v. Sacramento City Unified School Dist. (2003) 107 Cal.App.4th 1352, 1373.) Nor can a party create a triable issue of fact on the issue of duty through expert opinions, because again, the existence of a duty in a given factual situation is an issue of law for the court to resolve. (Vulk v. State Farm General Ins. Co. (2021) 69 Cal.App.5th 243, 259 fn. 6; Swigart v. Bruno (2017) 13 Cal.App.5th 529, 540 fn. 14.).