Could not load file or assembly System.Data.SqlClient

Hello,

I'm currently learning the ASP.NET Core-Web-API (.NET 6) system. I added a class-library (.NET Framework) (v4.8) as a DataAccessLayer to my project. There is a DAO class with a sql-query that uses Dapper and System.Data.SqlClient.

just for example:

var parameters = new { id };
using (SqlConnection connection = new SqlConnection("...")) {
  connection.Open();