How to Migrate Recent Changes within a branch

We have followed as much of the documentation as possible and have had no luck migrating the changes. Can you please clarify below questions on migration.

1. We can successfully migrate to another instance by copying the deploy build and changing the target instance. However, we have noticed this seems to be a catch all. It does not migrate the recent published changes but migrates everything in the workspace. It this the way it works with the seeded build package? Does it create a package for all changes from the workspace since the build package says from the main branch?

2. I have tried creating another branch in the workspace as the documentation suggest and making one change in that branch. I publish that change When I got back into our custom copy of the seeded build package, i can see other branches to select from but not the one I created to make the change. Why am I not able to find the branch i created in the workspace. See below that we followed.