#the last documentary about young nuns (a recent one) i saw did feature rings so i think the theory is safe

[sisterdivinium]

Consider: A) as "brides of Christ", Catholic nuns commonly wear rings to symbolise their attachment to Jesus;

B) the OCS nuns don't wear rings;

(notice, however, that the nuns Camila teaches "how to TikTok" do — if on the left — as does Yasmine and as do the others during the museum heist, wearing the colours of Yasmine's order)

C) the halo is basically ring-shaped;

Possible conclusion: their real attachment is to the halo bearer, who carries within her body the "ring" they might all potentially have to bear; this very ring embodies their vows in a single instance so none of them need individual bands. This one ring merges in itself all of the ones they might have worn, tying the sisters together, bonding them to one another, structuring their order to begin with.