Initial screen shows the following

[Quarnero]

@dav69

how to change Lock Screen password?

@dav69, please read carefully, user related one (not partition related one):

@amarok

Use the passwd command in terminal.

Please use numbers (for time being) only:
$ man passwd
$ q −− type q to exit

EDIT:

@dos

LUKS passphrase can be changed in GUI via the GNOME Disks app (which is installed by default).

[dcz]

Correct.
.

[dav69]

Thank you very much, I appreciate the help.

[amarok]

@Quarnero

Please use numbers (for time being) only

My user password for months now is alphanumeric, not just numeric. No problems at all so far.

[Quarnero]

Yes, I do recall now:

@dos

Well, we should probably lift that restriction now that phosh can handle alphanumerical passwords

[dcz]

You can change the decryption password in the “disks” application: https://source.puri.sm/Librem5/librem5-user-docs/-/issues/7#note_203026

[dav69]

Thank you dcz,
Highly appreciated.