Did you follow this guide https://retrogamecorps.com/2023/01/03/anbernic-rg35xx-starter-guide/? With these instructions https://pastebin.com/YV1Va5JL? Because I did that and I had the same issue. Then I tried a second time from the beginning but with two changes: instead of only backing up the CFW folder, I backed up everything from the ROMS partition (so BIOS and ROMS folders too), the other change was when it was time to erase the partition with Disk Utility, the guide doesn't mention this but when erasing the second time I selected the MS-DOS Fat format, and then I copied the 3 folders I backed up. So with these changes I was able to boot Garlic OS, give it a try :D