I'd be interested in more specifics here. I've been in a few bootloops with GrapheneOS early on but I've always been able to get out of them by keeping cool and not prematurely trying to reflash and wipe. Eventually the phone always booted (I think that it's due to the A/B partition system where eventually the phone will try to boot the other "working" partition again. But sometimes this would take a while).
It hasn't happened in a year though and I've been happily upgrading lately. I'm not saying you couldn't have run into a unique bug but I'd find it surprising if your phone was really left completely bricked except for reflashing/wiping it.
It was some time ago, so I unfortunately can't remember all the details. It occured during a normal system update that ran without problems at first, but when I rebooted the phone to finish the update it couldn't boot anymore (I can't remember the error messages). I don't know what exactly went wrong or was corrupted during the update. I definetly rebooted the phone multiple times and tried to fix the issue, but after some time I realized it was futile.
Maybe there still was a way to salvage it, but I really can't tell in hindsight.
This has happened to me when the battery ran out during the reboot/upgrade. One time I had to let it charge and reboot for a good 30 minutes and eventually it booted again.
I totally understand giving up there though as it sucks to not be able to use the phone for a while and is very inconvenient. Let alone if this happens at an inconvenient time/during a work day, etc.
It hasn't happened in a year though and I've been happily upgrading lately. I'm not saying you couldn't have run into a unique bug but I'd find it surprising if your phone was really left completely bricked except for reflashing/wiping it.