If you have a link that isn't working, your options are limited but practical:
Here is a report on why opening a MEGA link without its key is a cryptographic challenge and what your options are. The Problem: Why You Can’t "Bypass" the Key
: if you are trying to access your own account because you forgot your main password, you can use your Master Recovery Key to reset your password and regain access to your files. Note that this will not help you open someone else's shared link.
Many users search for "Mega key generators" or "decryption bypass tools." It is critical to understand that these are almost universally Malware and Phishing:
Websites claiming to provide keys or bypass decryption are often fronts for distributing malware or stealing browser cookies. Brute-Forcing: