The original 35xx released on 2023 and featured an entirely different chipset to the current line of anbernic xx devices. While it was supported by muOS when the device initially released, official support has since been dropped as the device is far outdated compared to the current line of xx devices. @xonglebongle above linked the last update for the 2023 rg35xx, and as he says no support will be offered as it is so far out of date unfortunately