Vulnerability when public link in aws s3 or get pre-signed url

By making you files public, you are allowing anyone/anything to have access to those files. If those files should only be access by authenticated users then you need to use pre-signed URLs and make your files private.

If the files you are storing can be view by authenticated and unauthenticated users, then making your files public in S3 is fine.

If you need a mixture of both, in my personal opinion its just easier to handle all your files in one method, and so I would change the files to private and use pre-signed URLs.

But you need to evaluate what your project is doing, what kind of files your are storing in terms of who should have access to them and implement your functionality accordingly.