PSA: Apple devices are facing another test-based bug similar to chaiOS and others. A specific string of characters received in a notification from Messages, Mail, and various other apps can cause iPhones, iPads, Macs, or Apple watches to lock up.
The characters causing the problem consists of the italian flag emoji and characters from the Sindhi language. MacRumors notes that bug seems to only occur through notifications containing the string. So just getting a text message with it has no effect, but a notification popup will crash the device or cause it to respring.
Jailbreakers are calling it CaptureTheFlag in the Apple r/jailbreak subreddit. Users say the text bomb first began circulating on Telegram. It has also turned up in tweets, but the originator is unknown. At least one jailbreaker has already issued an early fix, which is available on his Cydia repository.
Like other bugs of this nature we have seen, such as chaiOS and Effective Power, the malicious text does no permanent damage to devices. It's more of an annoyance until Apple issues a fix. Plus once found, trolls spam messages out at random trying to cause havok. Thankfully, an iOS beta tester said he tried the replicating the bug in the iOS 13.4.5 second beta, and it had no effect, so relief is not far out.
In the meantime, since the bug only seems to manifest with notifications, turning off all notifications should eliminate the problem. To do this on iOS, go to Settings>Do Not Disturb and toggle the switch on. By default, this silences calls as well. If you want calls to come through, scroll down to "Allow Calls From" and set it to your preference.
Do Not Disturb settings for macOS are located in System Preferences>Notifications. Do Not Disturb is in the left sidebar. For watchOS, Do Not Disturb is set to mirror your iPhone's setting by default, but if you need to get to it, go to the Watch app on your iPhone. Go into General and Do Not Disturb settings are right below Airplane Mode.