Note: I'm using VS for Windows so the UI is likely different.
Based upon this UI the language selection happens on the right side after you find the template you want. To the right of that is the language drop down.
However having said that VB isn't supported across the board on any platform yet. Given this old blog post VB isn't going to support ASP.NET Core APIs (not MVC) until 5.0. So at a minimum you'd need to target .NET 5. It isn't clear whether ASP.NET Core fully supports VB yet or whether it is just the APIs which means Razor and related UI stuff might not work with VB yet.