Device came with a 128GB SD card, but I filled it up with ROMs and ISOs in like a week. Just grabbed a 256 GB one - can I just copy the current ROM folder to the new card, and put it in with no issues? Or would I need to do something more to keep shit safe?
I have an Anbernic RG351P and the only complication was that I had to partition the card for the firmware and ROMs. That's not going to be the case for all of the handheld consoles out there, but be sure to check for your specific Retroid model.
Having firmware on the SD card is unique to Linux handhelds. Android handhelds are basically phones so the operating system is in the flash chip on the motherboard.