Wow! I didn’t know this! So you’re saying that instead of using slower and potentially unreliable WiFi, I could just use the iPhone charging cable to connect two iPhones and start the Signal transfer feature? Is this documented anywhere? Thanks.

I only ever learned about it from an issue about shitty backups on the Signal repo(s). I'm out at a bar so not about to dig up the link but it's probably easy to find on GitHub.