here are links to additional discussions from the time of the change: https://community.signalusers.org/t/mandatory-pin-is-signal-...

One of the few articles that talked about it at the time: https://www.vice.com/en/article/pkyzek/signal-new-pin-featur...

One of the many reddit posts by confused users who misunderstood the very unclear communications by Signal: https://old.reddit.com/r/signal/comments/htmzrr/psa_disablin...