Personal view, the Web Installer will avoid taking you into the “Lock” step because the user must be fully aware of the anti-rollback hazard.
(Aside – I would be interested to know if running the installer you were briefed about this hazard?)
The locking method and the anti rollback hazard is described fully on the install page Install /e/OS on a Fairphone FP5 - “FP5”.
Please take some time to read the “Red box” Caution and the “Details” section which is at first hidden on the page with a triangular device like this
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In this post (answered) Install /e/ on FP5 with newer Security Patches other users have talked though “what it means”.
Check out this answer Switching to E/OS permanently (Relocking / question) - #4 by aibd.