I think you’re missing the point.
As the OP mentioned, the installation guide indeed suggests it is possible to relock and even marks it as the final step when following the manual instructions. Following those steps: fails. Easy installer: fails but says it’s ok.
The thread you link, had you read it, suggests indeed that the solution to some of the issues I listed is to lock the device, sadly they do not mention how to achieve it. But AGAIN that’s what we’re mentioning here. Regardless how the people in that thread did it, it’s not achievable either by the easy-installer not by following the steps on the documentation. The documentation currently suggests BOTH that the relocking is the final step, AND that it’s ok to leave it unlocked.
More information for new users clarifying this “missmatch” , or rather, this awkward phone state, on what it means and what are the consequences of leaving it locked or unlocked, and specially making it clear in the docs that it’s currently not possible to re-lock the fp4 following the install instructions, would be much appreciated.