This is due to one of the breaking changes in EF Core 3.0 and that is: LINQ queries are no longer evaluated on the client So write the query in such way that EF Core can convert the expression into T-SQL or fetch the data into memory and then make your query.
There are three possibilities for getting the user in a component (a page is a component): Inject IHttpContextAccessor and from it access HttpContext and then User; need to register IHttpContextAccessor in Startup.ConfigureServices, normally using AddHttpContextAccessor. Edit: according to the Microsoft docs you must not do this for security reasons. Inject an AuthenticationStateProvider property, call GetAuthenticationStateAsync … Read more