When an uploader creates a public link, they toggle a setting that says "Remove decryption key from link." In that case, MEGA generates a link like: https://mega.nz/file/RfZAkQyT
Save yourself the hours of searching for "MEGA key crackers" and the risk of downloading viruses. Cryptography exists precisely to prevent what you are trying to do. How To Open A Mega Link Without Decryption Key