Ever since some maintenance release of Catalina, this should no longer be necessary.
Yes, that should be possible with certain operating system and EFI firmware combinations. See below.
I am still running macOS Catalina 10.15.7 (19H15) on my MacBookPro11,1, but updated from Boot ROM version 162.0.0.0.0 to Boot ROM version 427.0.0.0.0 that came with macOS Big Sur 11.0.1 (20B29).
Code:
sudo /usr/sbin/bless -firmware Desktop/Big\ Sur/MBP111.scap --verbose --recovery
Followed by a system shutdown (not restart), and immediate power on using the power button. You should see an Apple logo and progress bar; the firmware update should take about 1-2 minutes. Of course, this will not work with a patched, custom system firmware file; only with 'original' firmware files from Apple. I have not looked at the changes in the firmware prior to doing this; but the NVMe driver appears different (smaller?) and I will report back on any hibernation issues with the vanilla system firmware.
I didn't see details in this thread around where the EFI firmware files are located these days. The EFI firmware/Boot ROM/system firmware files are now hiding in
ee3ab6c04234b360dd8fca93c0ae49f957bf0843/AssetData/boot/EFI/EFIPayloads
from the archive
/Volumes/Shared\ Support/com_apple_MobileAsset_MacSoftwareUpdate/ee3ab6c04234b360dd8fca93c0ae49f957bf0843.zip
that was in the disk image
Install\ macOS\ Big\ Sur.app/Contents/SharedSupport/SharedSupport.dmg
.
Edit: Added the power off/power on instructions for clarity.