I have a 2017 13 inch MacBook Pro without a touchbar.
I upgraded from Mojave to Catalina and left the computer to do its thing. Now about an hour later, my computer seems to be off and won't turn on. It's connected to the charger and had a full battery when I started the update. Now it's basically dead. I've long pressed the power button for more than six seconds and tried short pressing it but nothing. I've tried this several times now.
I'm in lockdown and can't visit an Apple Store either.
EDIT: Steve Chambers' comment about resetting the SMC worked for me. When it restarted, it had Catalina installed. I still do not know what went wrong but hopefully, this helps others who might end up in the same boat.