Ah, you discovered attachments 🙂
The media library is not a file browser, and things placed in the upload folder don't just appear in the media library. Have you never wondered how WordPress saved the titles and captions for images?
When you upload a photo, WordPress creates a post of the type next to the physical file
attachment, As we know, posts have title, content, post meta, etc. The parent post is the post to which an attachment is attached or to which a post is uploaded (which is not reliable, however, since an image appears in more than one post) can).
One consequence of this are attachment pages that have their own template. When you add an image, you can link to its media page. You can use this as an opportunity to add comments, show more details, etc
As Jacob said, these are normal and have always existed in WordPress and are intentional. It is not something that has occurred as an error, it is not strange, and it is present in some form on every WordPress site.
You can get them in code by getting an attachment permalink or using the dedicated API function. You can also simply click the Attachment View Page link in an attachment view:
You can even edit the permalink on the attachment editing page:
On my site there is even a yoast SEO box to optimize the attachment page for rankings