When using FileVault, and you are logging in, is your login password also the key that decrypts FileVault? And if that’s true, when you turn FileVault on, does it use your login password to seed the encryption? And if that is also true, does it mean that the longer and more random your password is, the stronger the encryption will be? Also, while logging in, does the progress bar represent that decryption is underway?
Just want to have a better understanding of how FileVault works.
I believe the way it works is that the key for encryption is always complex and strong. Logging into your user account gives your account access to that key. So your user account password is not your key and the strength of the login password doesn't affect the strength of FileVault encryption.
If this is important to you, I would seek out a security expert who knows about FileVault and ask them too. I've never researched this specific aspect of FileVault and if you need a definitive answer I'd try to dig deeper.