Hello, @dylee
Thanks for your interest on S32G3RDB
1. For booting the board, as described RDB3 USER Guide, the following 4 methods are supported, including SD/eMMC/QSPI/Serial.
2. If specially booting Linux(from Uboot), then from my experience, it may be supported from USB flash driver and/or SSD(with PCIe or M.2 interface). But sorry that there seems no related documents which targeted for these settings.
Apologize for your inconvenience.
BR
Chenyin