Hi,
I am 99.9% sure it won’t work on an FP4. I did see a dump of oem commands for the FP4 and “allow-flashing” was not one of them. There was an interesting one about rollback protection though, that the FP5 did not have. I found the FP4 oem commands dumped by someone in a massive thread on this forum somewhere.
I actually don’t know why it bricked. I tried to install Iode and it just said “your device is corrupted” then went to Fastboot. After thiat it would only go to fastboot. It could be rollback protection, or it could be my Fairphone does not trust the Iode keys (its a Murena one).
I do not think it wipes data, I’m not sure. Since I was just happy to unbrick I did a full restore to FPOS including wipe data, so I could get a clean slate to start from.