How can I change my passphrase to the encrypted MacBook Pro boot volume?

Using a second administrative account with the permission to unlock the boot volume I could remove my user ID from FileVault and add it again:

% sudo fdesetup remove -user harri
% sudo fdesetup add -usertoadd harri
Enter the user name: administrator
Enter the password for user 'administrator':
Enter the password for the added user 'harri':

On the second step I could set the new passphrase.

Found it on https://community.jamf.com/t5/jamf-pro/adding-user-to-filevault-using-fdesetup-and-recovery-key/m-p/209230

Neither would I like to change the recovery key, nor did I forgot my password. The problem on my Macbook Air is, I have to enter my old password to decrypt the boot volume, and later my new password to login.

On the Macbook Pro M1 there is only one login prompt at boot time. It accepts the new password to decrypt the boot volume and logs me in right away, without asking again. I had used this Macbook to change the password on my network account.

So how can I keep the passphrase to decrypt the boot volumes and the login password of my network-wide account in sync for #Macs > 1?

As written before, I haven't forgotten my passwords. I did not use my icloud account to setup FileVault, either. Both Macs were initially set up by my colleagues from the IT department, including FileVault for the boot volume. Nor did I change my icloud login password to run into this problem in first place. My account is managed in Active Directory and cached on the Macbooks, AFAIK.

As you noted, the FileVault passphrase is not synced between devices. As my Macbook Air shows, the Filevault passphrase is not bound to the login password. And since I could change both (network-wide password and locally managed Filevault passphrase) on the Macbook Pro somehow, there must be some way to change this passphrase after login, without touching my network password.

So how can I change my passphrase for the boot volume in Filevault?