Thank you very much John. This pointed me in the right direction.
For anyone wondering, I ended up adding a meta field to the newly created attachment from the upload using update_post_meta after form submission.
And then pre-filtered the posts query on the upload.php and admin-ajax.php (both media library access points) for attachments without the meta field using pre_get_posts().
Thank you! 🙂
Boom! Thanks a lot Joshua.
Just dropping a big thank you because this is EXACTLY what I needed to solve.
Thanks!