New jetpack bricked my nx?

There is actually QSPI memory on the module itself, and the SD card release version has to be compatible with that. One must often flash the QSPI once with the more recent release, and then SD card upgrades would typically work for several releases before QSPI needs another flash. Some explanation:
https://forums.developer.nvidia.com/t/topic/220018/5

“Bricked” means the unit is dead and cannot be flashed, and that is indeed a very very rare event. You have to flash the module too, and not just the SD card in some cases, and this will likely solve the problem.