How to create one single stored procedure for all select, insert, delete and update operations in SQL Server

This way

CREATE PROCEDURE [dbo].[Customers_CRUD]
      @Action VARCHAR(10)
      ,@CustomerId INT = NULL
      ,@Name VARCHAR(100) = NULL
      ,@Country VARCHAR(100) = NULL
AS
BEGIN
      SET NOCOUNT ON;
 
      --SELECT
    IF @Action = 'SELECT'
      BEGIN
            SELECT CustomerId, Name, Country
            FROM Customers
      END
 
      --INSERT
    IF @Action = 'INSERT'
      BEGIN
            INSERT INTO Customers(Name, Country)
            VALUES (@Name, @Country)
      END
 
      --UPDATE
    IF @Action = 'UPDATE'
      BEGIN
            UPDATE Customers
            SET Name = @Name, Country = @Country
            WHERE CustomerId = @CustomerId
      END
 
      --DELETE
    IF @Action = 'DELETE'
      BEGIN
            DELETE FROM Customers
            WHERE CustomerId = @CustomerId
      END
END