I never held the power button down for 20 seconds, but I did that just now a few times, and still not getting the phone to boot. No, the enter the disk encryption key is not coming up.
I should mention that when I hold the power button, the green dot light on top does come on and the phone does do the little vibrate like it’s about to boot, but just never gets to booting; never even see the Librem 5 logo.