I'm having the same issue. I have Recalbox on an 128GB SSD and it works fine with my other Raspberry Pi's that are not in the NesPi4 case. I've tried the SSD in the game cartridge as well as in a USB slot with SATA to USB adapter. Every time it loads to a black screen and does nothing. I've even attempted putting Recalbox on a MicroSD card as a test and ended up with the same results.
There are no issues loading the Raspberry Pi OS or Ubuntu 20.10. I can load them with USB and with a MicroSD card no issues.
If anyone has a fix, please do share.
Thanks!
