Yes, here you have Briar bumping up against the inability to run any fully decentralized mobile communication software on iOS. Seems like a serious limitation on the part of iOS at this point given trends towards decentralization in general.
The worst part is that an inactive background TCP connection is mostly free (of course, a Tor client is slightly more involved), so there is exactly 0 reason to forbid it, as long as apps are reviewed properly for abusive behavior (they are not).