Startup1.cs

public void Configure(IApplicationBuilder app)
{
   app.UseOwin(x =>
   {
        //Use Owin here
        x.UseFirstPipelineMWThatIsOwin();
        
        //Use ASP.Net Core pipeline inside UseOwin
        app.Use((context, next) => {
              context.Request.Headers.Add("CUSTOM", "BOB");
               return next();
         });
                  
        //Use Owin here
        x.UseMyOwinMW();
  });
}

Startup2.cs

public void Configure(IApplicationBuilder app)
{
    //Use Owin here
    app.UseOwin(x => x.UseFirstPipelineMWThatIsOwin());
    
    //Use ASP.Net Core pipeline
    app.Use((context, next) => {
          context.Request.Headers.Add("CUSTOM", "BOB");
           return next();
     });
     
    //Use Owin here
    app.UseOwin(x.UseMyOwinMW());
} 

Startup3.cs

public void Configure(IApplicationBuilder app)
{
    //Use middleware converted for owin to aspnetcore pipeline here
    app.UseFirstPipelineMWThatIsConvertedFromOwin());
    
    //Use ASP.Net Core pipeline
    app.Use((context, next) => {
          context.Request.Headers.Add("CUSTOM", "BOB");
           return next();
     });
     
    //Use Owin here where we have to at the bottom
    app.UseOwin(x.UseMyOwinMW());
}