Yep, sysNAND; I put that at the top of the instructions.With EmuNAND or sysNAND?
The instructions on the gateway website say to use sysNAND, so I'm going to assume you mean sysNAND too.
Whenever I press SELECT after booting into sysNAND I get 'filesystem error'. (I've tried both exfat and fat32, and two different microSD cards)
When I boot into gateway mode normally (no NVRAM install, no holding 'B'), pressing SELECT works as it should
Background: Both emuNAND and sysNAND are on untouched 9.0.0-20E. I've just been following the gateway guide so far. (Ignoring the Restoring NAND and updating emuNAND part)
That's odd that the rom menu works in emuNAND, but not sysNAND. Try this tool: https://gbatemp.net/threads/gateway-3ds-microsd-tool.369165/ to see if that solves your problem.