Mac won't power on after Tahoe upgrade

I think you need to perform a DFU Firmware Revive to update the security enclave & system firmware. This shouldn't affect the data on the internal SSD (not sure what happens if the process fails to complete successfully though). I saw another post on this forum regarding an M3 computer where Apple tech mentioned to the user that this will update the system firmware which may be the blocking point on the OS upgrade to Tahoe.

If the DFU Firmware Revive does not work, then you will need to resort to a DFU Firmware Restore which also resets the internal SSD & pushes a clean OS onto the internal SSD destroying all existing data on the internal SSD.

This process requires access to another Mac running macOS 26 Tahoe, or possibly macOS 15.x Sequoia.

How to revive or restore Mac firmware - Apple Support

Wyattburp wrote:

I upgraded from Sequoia to Tahoe today. The update was stuck on "2 minutes remaining" for 30min, I stepped away and when I came back, the screen was black. I've tried to force restart and every combo of command, option, shift, etc. to no avail. Not a single indication that the laptop is even trying to start up. It's a MacBook Pro with M3 chip.

The screen often goes black a couple times near the end of the install—before it presents you with the Tahoe splash screen— if you interrupted that I could see causing as an issue.

those "estimated" times can be woefully inaccurate.

You can try Recovery and reinstall the macOS

How to reinstall macOS

Recovery (both M1/M2/M3/M4 and Intel) — How to reinstall macOS - Apple Support

if no luck—

Call Customer Support (800) MY–APPLE (800–692–7753)

or on line https://getsupport.apple.com/

or call AppleCare Support at 1-800-APLCARE (800-275-2273)

Outside the USA—Contact Apple for support and service by phone

See a list of Apple phone numbers around the world.

Contact Apple Support - Apple Support

Wyattburp wrote:

I'm not able to get to the recovery mode. The mac doesn't respond to holding the power button - it simply does nothing.

I would verify it is shut down—

You can always force quit a shutdown by holding the power button/TouchID for ~6-10 sec.

Force Shut down your Mac. The Caps lock should not respond with the green light.

Then just press the power button once and see if it comes to life...

Log out, sleep, wake, restart or shut down your Mac

Shut down or restart your Mac - Apple Support

Wyattburp wrote:

Thank you, it's def shut down. I've made appt with the Genius Bar

ref: If your Mac doesn't turn on - Apple Support

if no progress I posted the call in Apple Support numbers above. Go from there.