SOLVED!
Date: 02/09/2021
My devices: iMac mid-2015 in macOS Big Sur. iPhone 8 with working TouchID but Home Button broken.
Managed to get through DFU and setup as new device, yet failed to restore from an old backup, stuck at the “press home button to upgrade” screen. Tried several times with enabling either VoiceOver or Assistive Touch before restoring backup, yet all failed. I BINGO by disabling both TouchID and passcode to unlock the phone, no more “press home button to upgrade” screen after all, got all data saved.
Here is the walkthrough:
# connect the iPhone to Mac.
# Press and release of Volume Up button, then press and release of Volume Down button. Press and hold the Power button, you will see power off and back on, release when you see Recovery Mode screen. (a cable pointed to a mac)
# On Mac side, Finder should prompt update or restore your iPhone. Click restore, it started downloading Firmware automatically, which brings iPhone back to factory default.
# After restarting, setup as new device. (As my iPhone had assistive touch enabled here, no problem get through the Hello screen).
# Go to Setting > Touch ID & Passcode, uncheck (use Touch ID for) iPhone unlock, then Turn Passcode Off.
# Back to Finder, Location > your iPhone, hit Restore Backup under General section.
# After restoring backup finished, no “press home button to upgrade” screen this time, direct me to Hello screen with Assistive Touch enabled.
# You know what to do.
I hope it helps.