Catalina Update bricked my macbook pro 13

Boot into Recovery (Command R) and from the dropdown menu: Utilities>  Disk Utility> run the First Aid on your Macintosh HD (and the "Macintosh HD-Data" volume as well if Catalina) If errors are found and repaired, run again until no errors reported.

Recovery: https://support.apple.com/en-us/HT204904

That's all you can do. Of course there is no harm in repeating Reset the System Management Controller in what's likely to be an exercise in futility.

That brings you to the conclusion "If you still need help, please contact Apple Support."

The Caps Lock LED should be available shortly after it's powered up:

Lights, such as from a backlit keyboard, Caps Lock key, or sleep indicator light

There isn't much else to distinguish life from death on a MBA.

I did find out the MacBook Air was able to respond to keystrokes, but the only combo I knew were registering were for Revive/Restore of the T2 Firmware noted in this article:

Revive or restore Mac firmware in Apple Configurator 2

I held the keys while Air was connected via its charging USB-C cable to my iMac Pro which had Configurator running. A box showed up for the Air with a DFU in it, it was very exciting! The only sign of life of the Air was on the iMac's screen!

I was able to Restore (I meant to do a Revive, but was reading the Restore instructions) the Firmware. Part of the Restore process is erasing the SSD, but we do run two Time Machine backups so there were several to choose from after the Internet Recovery reinstall of Catalina. Configurator was not great at giving feedback of what was happening with the Air, and it did tell me that there was some sort of error and that it hadn't worked. A few moments later the Air booted into Internet Recovery mode.

There were several adventures with the Time Machine restore of the Air, but it is now up and running as good as ever.

I was very grateful that the macintouch.com web site had a description of the bricking issue and it agave a link to the instructions linked above. Everything I saw up to that point, including a text chat with AppleCare support, sounded like my only option was to send it out for repair.

I understand your Mac won't turn on. Please read If your Mac doesn't turn on - Apple Support.

Going down that road is likely to get this Discussion abruptly removed. Personally I doubt it, but... desperate times, desperate measures.

Just so you know what could happen, every once in a while someone comes to this site describing what happened when they tried to replace a battery on their own. Sparks, smoke, dead Mac, then they come here asking what now. So, proceed on the basis of that knowledge.

"I have the feeling that that Catalina patch is going to unearth a number of other bricked machines. Hopefully I'm the only one."

Oh no don't feel that way. Catalina actually has been a very successful upgrade. There are always small bugs but I had a 2018 MBP I upgraded to Catalina flawlessly. My 16" MBP runs Catalina without issue. Your issue is a rare occurrence. It's Apple's OS being installed on Apple's computers. "Bricking" generally is caused by corrupt files already installed on the user's computer that caused an install failure or it's a hardware problem. Other issues with failed installs come from temporary loss of wifi during install (if done through internet recovery) or temporary loss of power during the install, which could be a possibility of hardware failure. But OS's generally don't brick computers. Many thousands of people have upgraded to Catalina and there's no known reported issues of bricking.

Just to be clear, when you said "Catalina Patch", is this some unauthorized patch used to install Catalina or is this a genuine OS upgrade directly from Apple with NO hacks used to install it? Is your Mac a Catalina-supported model?

Thank you for bringing this to the forum's attention. I didn't know of any supplemental update. I just installed it on my 16" MBP and everything went 100% smoothly. I just press the UPDATE button and left alone. Took 8-10 minutes to complete and I was back on the desktop. This is not a widespread issue.

I installed the newly released 10.15.4 Combo on all eligible Macs in our home on Wednesday night with no issues.

Thursday evening my wife's Air still showed the update in System Prefs and clicked to install it. She said the dialog box said it was normal for the screen to go black, but it didn't say it'd never come back!!!

Her less than 18 month old Air is now officially bricked. Unresponsive to all attempts to remind it of its mission on earth. A stellar machine until that fateful click.

It is funny how the "my Mac is unresponsive" support document says to listen for fans, drive noise, boot chime, other normal computer sounds- this Air never had any of those sounds! ::grin:: It needs some lights for battery charge level, MagSafe adapter light, something to let us know anything about what's going on with it.

Sad to find out we'd not gotten Apple Care. I was traveling a lot the several months after she got it and don't remember what happened, but we apparently each thought the other would have taken care of that. Curious to see how that all works out when we can eventually take it in when we can go to an actual Apple Store again.

Glad to here you were able to resurrect you Mac. I'm in the exact same spot with my 2018 MBP completely bricked. FWIW, I actually tried to "Revive" rather than "Restore" and it didn't work. I haven't tried "Restore" yet since my back up is two months old. I'm really disappointed in Apple that an incremental software update could do this to people's Macs. And there seems to be no official acknowledgment of this major flaw.

Just contact Apple Support over the phone. They will set you up for a repair and you can mail it in for service.