How specific/secure/selective is Touch ID?
Apple, iOS Security, November 2018, p. 10


  The probability that a random person in the population could unlock
  your iPhone is 1 in 50,000 with Touch ID or 1 in 1,000,000 with Face ID. This probability increases with multiple enrolled fingerprints (up to 1 in 10,000 with five fingerprints) or appearances (up to 1 in 500,000 with two appearances). For additional protection, both Touch ID and Face ID allow only five unsuccessful match attempts before a passcode is required to obtain access to your device.