What is the correct way to deal with git submodule commits?

Question

git

Separated part of the project into a submodule.
Made changes in the submodule and pushed to the submodule repository.
I started making changes in the submodule further, made a temporary local commit, which I am going to overwrite, only in order to switch to another branch of the main project . git statusshows no change.
I return to the root of the project - git statusit shows that the folder with the submodule has been changed (Changes to be committed) and duplicates below that the submodule has been changed (new commits) (Changes not staged for commit) .
In order to switch to another branch, do you need to make a commit in the project as well? And if you make a simple commit, will there be a message that says that there are new commits in the submodule (until you push)?
Tried git stashit, it says No local changes to save
Do you always have to commit in the main project, along with a commit in a submodule? If yes, then it is clear why a separate branch is created in the tutorial..