EFCore SqlClient error LocalDB

From .Net standard 2.0, we can use the SQL Server database in a UWP app, but your UWP app must configure target version and min version 16299 or more higher version. You can change them by right click your project => Properties => Application tab.

You can see the document Use a SQL Server database in a UWP app and the sample: https://github.com/StefanWickDev/IgniteDemos/tree/master/NorthwindDemo

Besides, here is also a similar thread you can have a reference:

How to connect to SQL server database from a Windows 10 UWP app

---Update---

Currently, UWP app doesn't support the LocalDB on 16299 and 17134. But in my test, LocalDB can work well in WPF app and Console app, this is my connect string:

        public string LocalDBConnectionString = @"Data Source=(localdb)\MSSQLLocalDB;
Initial Catalog=master;Integrated Security=True;
Connect Timeout=30;Encrypt=False;
TrustServerCertificate=True;
ApplicationIntent=ReadWrite;MultiSubnetFailover=False";