The SMC reset process has changed on Macs that have an Apple T2 chip, including iMac Pros and 2018 MacBook Pros.  Apple has posted this new SMC reset process for these models:

  • Choose Apple menu > Shut Down.
  • After your Mac shuts down, press and hold its power button for 8 seconds.
  • Release the power button, then wait a few seconds.
  • Press the power button again to turn on your Mac.