Salesforce began to phase out the classic Notes and Attachments Related list in favor of feature-rich Files and Enhanced Notes. Notes will be replaced by Enhanced Notes and Attachments will be replaced by Files. The Notes and Attachment related list will no longer have an upload or attach button. Users will be required to migrate to and adopt Salesforce Files.
Benefits of Using Files and Enhanced Notes :
More robust sharing rules for each uploaded file.
Publish the uploaded file publicly.
Use rich text in your notes.
Use most files without downloading.
Simple drag and drop feature.
Larger file size up to 2 GB.
Collaboration via chatter feed.
Example of a Notes and Attachments Related list on a record :
The New Files and Notes Related List :