Linux version is 20.2
Can you read the above? The spacings are gone after I saved the post, so I put the semicolons there.
Yeah I can read it but it doesn't show me anything about in an encrypted homedir, but I was able to install a virtual system with Linux Mint 20.2 that has an encrypted home folder and when I change the password of my user I get a login loop as well. I see this in the system syslog.
Jun 14 08:28:44 mint lightdm: pam_ecryptfs: Passphrase file wrapped
Jun 14 08:28:44 mint lightdm: Incorrect wrapping key for file [/home/tux/.ecryptfs/wrapped-passphrase]
Jun 14 08:28:44 mint lightdm: Error attempting to unwrap passphrase from file [/home/tux/.ecryptfs/wrapped-passphrase]; rc = [-5]
Jun 14 08:28:44 mint lightdm: pam_ecryptfs: Error adding passphrase key token to user session keyring; rc = [-5]
Jun 14 08:28:44 mint systemd[1]: Stopping Session c14 of user lightdm.
Jun 14 08:28:44 mint systemd[1]: session-c14.scope: Succeeded.
Jun 14 08:28:44 mint systemd[1]: Stopped Session c14 of user lightdm.
Jun 14 08:28:44 mint systemd[1]: Started Session c15 of user tux.
Jun 14 08:28:44 mint lightdm[2522]: Signature not found in user keyring
Jun 14 08:28:44 mint lightdm[2522]: Perhaps try the interactive 'ecryptfs-mount-private'
Jun 14 08:28:44 mint pulseaudio[2457]: Unable to set sw params: Permission denied
Jun 14 08:28:44 mint pulseaudio[2457]: Failed to set software parameters: Permission denied
Jun 14 08:28:44 mint pulseaudio[2457]: Error opening PCM device front:0: No such file or directory
Jun 14 08:28:44 mint lightdm[2502]: Error writing X authority: Failed to open X authority /home/tux/.Xauthority: Permission denied
When I then change it back to the old password I am able to login with that user. So that verifies again that your original/old password is used to decrypt your homedir and when having changed that it caused the login loop. I also tested this out on the latest version of Mint, 21.3. And there when I do the same and try to login with the new password I am able to access the homedir because the encryption is done differently and not with the user's first/original password.
So long story short, with Linux Mint 20.2 and you have an encrypted homedir and you change the password because you forgot the original one you will have no way to regain access to your files because the homedir is encrypted and uses your old/original password as a passphrase and causes a login loop because the home folder can't be decrypted.