According to Retro Dodo, the key difference here is that the Android OS has been removed (the RG353P allowed you to dual-boot, choosing either Android or Linux).
Outside of that, we don't have any solid info on the specs, but it might be safe to assume it's using the same quad-core RK3566 chipset as the RG353P. It might also be prudent to expect the RG353PS to retail for slightly less than the RG353P did.
"Factor in 5G Wifi, Bluetooth 4.2, HDMI-out, two USB-C ports and a 3500mAh battery that's good for around 4-6 hours of gameplay, and you're getting a lot of bang for the $140 the RG353P costs to purchase," is what we said when we reviewed the original RG353P back in August of 2022. "Does all of this add up to a machine that can really be considered to be the RG351's successor? Unless you're super keen on the idea of having the ability to boot into Android, then perhaps not, but there's no denying that the RG353P is an excellent entry point into the world of portable emulation – and the fact that Anbernic has been brazen enough to copy Nintendo's design means it looks great and is comfortable to use, as well."