I got the same problem here. Tried everything: Reset NVRAM, Reboot, Clean install Catalina then try again, boot from external disk, turn of FileValt, Firewall.....
And still got stuck at 12mins. MacBook 16 2019
kh4inguyen
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Hi all,
I fixed this by:
Open Terminal. Paste and enter:
sudo nvram IASUCatalogURL=https://swscan.apple.com/content/catalogs/others/index-10.16seed-10.16-10.15-10.14-10.13-10.12-10.11-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog
You may need to enter 2 time if you got the error.
After that, rerun the installer --> It worked.
After done upgrading, you should update the nvram back:
sudo nvram -d IASUCatalogURL
Source: mrmacintosh.com/big-sur-11-0-1-rc2-full-installer-an-error-occurred-installing-macos