My Legion 7i 2021 BIOS is screwed up and I don’t have a BIOS backup, how can I try to restore it? (Mileage may vary on other Legions with different BIOSes)
Well… you need a 3.3V SPI programmer like the CH341A and you need to know how to use it, if you don’t know this guide isn’t for you. You can build a config-less, serial-less BIOS using the one provided by Lenovo following these steps

First of all, it’s better to dump the current non-working BIOS using the SPI programmer.
DUMP IT and VERIFY the dump with the software you’re using (I used NeoProgrammer 2.2.0.8)
You can recover your own serials/os keys from the broken BIOS, there will be another guide for that, but you need to have a good dump for that.

• install HxD and 7-Zip
• Start the downloaded .exe and select to extract it in a convenient folder (eg: desktop/bios/)
• Open the folder, you will find an .exe file (eg: BiosName.exe)
• Extract it with 7-zip using task menu function (right click on the file → 7-Zip → Extract in “BiosName”) don’t mind for errors, they are normal.
• Open the new folder just created, there is a BIOS.fd file, that is the BIOS file we want to trim to 16 MB, it’s larger due to the fact it contains firmwares for other ICs and programming instructions.
• Start HxD and open BIOS.fd file
• Ctrl+E, start: 97D050 | length: 1000000 | Hex
• Ctrl+C, Ctrl+N, Ctrl+V, Enter, Ctrl+S
• Save this file in the convenient folder with a proper name (eg: lenovo_clean.bin)
• You can now flash this file using a programmer to the BIOS IC, you will lose any config/serial/os key, but at least it should boot

— @LABØ