So I feel like I need to update this thread because there was some debugging required to get it working:
First off, I think the device telling me to press a button in order to shut it down (which happened after running a multitude of commands in fastboot) was fastbootd crashing. It almost felt like killing PID 1: the text was way too small to be intentionally user-facing and also the message IMO doesn’t make a lot of sense after running a `getvar all`.
Also, the device sadly did not work as intended: I thought everything worked fine until I woke up to an alarm that only vibrated. I played some music and realized audio wasn’t working at all. I then tried restarting only to be met with the bootup stuck at the Iode logo for way too long just like at first boot.
Despite me “successfully” flashing the device twice at that point and being hit with the same issue every time I do, I downloaded the `-ota` file for Iode on the FP6, went into the lineage recovery and side loaded it via adb. Rebooted and the device started in less than a minute and fully functional.
There have been some reports about fastboot being a little picky on the FP6, so I am going to assume that this is probably on them and not Iode. The way fastbootd responded to my commands was flakey at best.
More info: between the two successful fastboot flashes (which both resulted in a broken OS), I changed: USB cable, host, fastboot version and USB version. After the first flash, I did not wait long enough during boot for anything to happen and tried re-flashing after staring at the logo for half an hour.
Maybe someone can do something with that information 
CodeSalat