Which special back xmogs are open to everyone?

[Krek01]

As the title suggests, which of the new special transmog backs are available to everyone for use and looting, regardless of Covenant?

I know for a fact that the containment packs from Maldraxxus rares (Bubbleblood and the Oily Invertebrate) can be found and used by everyone, but what other special backs can be found anyone, no matter what Covenant they chose?

[jeokaleo]

Is it possible to unlock and equip all the transmogs from the covenants even if you want to transmog the gear from a covenant you've not currently chosen? I want the venthyr transmog but i like the kyrian ability better. Will I be able to unlock the venthyr transmog, then chance to kyrian, but still transmog my gear to the venthyr set. And is it possible to do this for every covenant transmog as Speed Test well?

[haiyken]

Is it possible to unlock and equip all the transmogs from the covenants even if you want to transmog the gear from a covenant you've not currently chosen? I want the venthyr transmog but i like the kyrian ability better. Will I be able to unlock the venthyr transmog, then chance to kyrian, but still transmog my gear to the venthyr set. And is it possible to do this for every covenant transmog as well?

No, once you change covenant, the transmog you unlock gets desactivated. You still technically have it, meaning if you go back it's still available, but it's not usable when you're in another covenant.

As for the OP, I don't know of any back pieces available in Shadowlands apart from the ones you listed. The only ones that comes to mind are the Wrathion backpack and the Recruit a Friend backpack.

[Wries]

Is it possible to unlock and equip all the transmogs from the covenants even if you want to transmog the gear from a covenant you've not currently chosen? I want the venthyr transmog but i like the kyrian ability better. Will I be able to unlock the venthyr transmog, then chance to kyrian, but still transmog my gear to the venthyr set. And is it possible to do this for every covenant transmog as well?

Not OP's question but you can only mog into backs (and weapons etc) that are affiliated with your currently chosen covenant. However, you get to keep any currently applied mog when you switch.

[Jutath]

Only one I know of is the green ooze backpack from Bubbleblood.