Accessory Innovations is back in 2021, with a character plush backpack that is for sale at Target online (and probably in some stores too) This is another of those 'the doll IS the backpack' so the back of the body unzips so you can put small items. The red nylon adjustable backpack straps are on the back of the plush doll so...if you actually put the straps on, all the doll spikes would be poking you so it's unlikely to be that comfortable. The space for items is also really small so it wouldn't be super useful.

So it has going for it: Can't store a lot of stuff, is not comfortable to 'wear', and is large & impractical to carry plus being sort of costly at 30 dollars? Well...it hasn't much to say for itself. However, the likeness is okaaay at least? The shoes are detailed and good/big. The arms are long enough & he does not suffer big body. The ears are a tad low on the head, but they do have the borders & his spikes are all pointed properly/large enough. The eye is a big large but it is well shaped & everything looks normally/stuffing levels. Accessory Innovations is clearly capable of doing a good job on things, but it just seems to kind of be 'why make him into a backpack'? Seems odd.
There is also a Knuckles one of this released at the same time, but it is sadly seen over on Mutant Gear.