UWP cannot connect to local SQL Server

I'm creating a simple UWP application working together with my local DB server I set up with SQL Server Management Studio.

I can successfully set up a connection in the server explorer and run queries in the DB:

However when I run the application I get an error when the connection is being established:

System.Data.SqlClient.SqlException HResult=0x80131904 Message=A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 25 - Connection string is not valid) Source=Core .Net SqlClient Data Provider

I'm not sure if it's a problem with the connection string or what else it could be. I checked the firewall settings and everything seems to be fine. The SQL server settings also allow for remote connection.

Which SQL Server version is running?

Have you tried with the following connection string format?

Data Source=.\\MSSQLServer;Initial Catalog=PapaDario;Trusted_Connection=yes;