I’m using the modern library but once I’m uploading a new file it already getting Metadata. When I upload a new file, I want it to be shown that his fire requires attention, so that the user goes and fills the attributes
It is by designer that it doesn't prompting for Metadata in the New Document Library Experience when you upload a document.
You can add the Metadata by using "Quick Edit" or choose a document and choose "open the details panel".
For more detailed information, refer to the following article: