Something is wrong. Usually, when you switch branches, unprocessed files are listed with you without any notice. That is why they are called "without a trace." However, you say files without a trace will be overwritten. This means that you created an unconventional file in a new branch that already exists in the main branch. This means that you need to decide what you want to do: what you need to save. It's not about getting git to do something; it's a matter of when you don't understand what you want.
Assuming you want to somehow resolve the conflict between two copies of the same file, you can do
git checkout feature_branch
git stash
git checkout master
git stash pop
And then eliminate the conflicts that arise.
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