[Samsung Galaxy S21 FE] Williamtung:
Your warranty is now void.
If you root your device, Your KNOX status will be tripped.
You can still pass the safety net after you root if you follow the instructions.
I am not responsible for bricked devices, dead SD cards although it is not really possible
Please do some research if you have any concerns about doing this to your device

How to flash official firmware? (not the root and unlock bootloader part!)

You will need:

A Galaxy S21 FE and common sense

Samsung Odin (the flashing tool of the official firmware)

https://dl2018.sammobile.com/Odin3-v3.14.1.zip

You need to extract the zip file and you are going to use the file Odin3_v3.14.1.exe inside the folder.

Samsung Android USB Driver for Windows

Samsung Android USB Driver | Samsung Developers

You need the driver only if you are developing on Windows and want to connect a Samsung Android device to your development environment over USB.

developer.samsung.com

Double-click and install the exe file.

Samsung Official Firmware

Release 1.0.3 · zacharee/SamloaderKotlin

Contribute to zacharee/SamloaderKotlin development by creating an account on GitHub.

github.com

Download the platform you want to download to. (Windows)

You need to extract the zip and double click open the file Bifrost.exe inside the folder.

You need to fill in the Model, Region, press the Check for Updates button and the Download button.

How to find the Model: on your phone → Settings → About Phone → The third row says the Model number and you need to remove the part with the part of /xx, for example, SM-G990B/DS and you only need to type SM-G990B

How to find the Region: You can check the Region at this link https://samfrew.com/model/SM-G990B/

You need to find find a three-letter word depending on your carrier and country and type it in Bifrost, for example, EVR

Press the Check for Update button and download it with the Download button.

Put it to a place you can easily find, ie. Desktop.

After downloading it, find the file SM-xxxxx_x_xxxxxxxx_xxx.zip.enc4 on the place you put it and change the document format from .enc4 to .zip. Then, double click and extract the file.

Open Odin3_v3.14.1.exe and turn off your phone. Connect a side of your USB to your PC/Laptop, keep pressing volume up and down together until you go to Download Mode. Put another side of the USB into your phone. When you arrived at Download Mode press volume up. Go back to Odin3_v3.14.1.exe:

-Click on BL and select BL_xxxxxxxxxx.tar.md5

-Click on AP and select AP_xxxxxxxxxxx.tar.md5

-Click on CP and select CP_xxxxxxxxxx.tar.md5

(If you want to keep your data don't flash CSC).

-Click on CSC and select CSC_OMC_xxxxxxxxxx.tar.md5

-Click on USERDATA and select HOME_CSC_OMC_xxxxxxxxxx.tar.md5

Press Start to flash the firmware, after done, your device will automatically reboot to the system.

How to unlock the bootloader?

Go to your phone → Settings → About Phone → Software information → Press Build number 6 times until you see the notice “You’re now a developer”

Go in Settings → Developer options → enable OEM unlocking

Power off your phone first. Then, connect a side of your USB to your PC/Laptop, keep pressing volume up and down together until you go to Download Mode. Put another side of the USB into your phone.

When you arrived at Download Mode, long press volume up until you see the black screen. Confirm to unlock the bootloader and you will erase your device.

How to root your phone?

After you unlock your bootloader, you set up your phone and make sure you do not sign in google account first. Install Magisk https://github.com/topjohnwu/Magisk/releases/download/v24.1/Magisk-v24.1.apk on your phone. Oh yes, in case you do not know, you need to allow the app to install apps so that you can install the apk.

Transfer AP_xxxxxxxxxx.tar.md5 in the firmware you download from your PC/Laptop to your phone.

Open Magisk on your phone and press the install button in the Magisk column. Select 'Select and Patch a File', 'Let's Go' and find the AP_xxxxxxxxxx.tar.md5 and select it. You can have a cup of coffee if you like when you waiting for the patching of the file.

After finishing the patching, you need to transfer the file magisk_patched-24xxx_xxxxx.tar in the Downloads folder back to your PC/Laptop.

Turn off your phone. Connect a side of your USB to your PC/Laptop, keep pressing volume up and down together until you go to Download Mode. Put another side of the USB into your phone. When you arrived at Download Mode press volume up. Open Odin3_v3.14.1.exe on your PC/Laptop:

Click on BL and select BL_xxxxxxxxxx.tar.md5

-Click on AP and select magisk_patched-24xxx_xxxxx.tar

-Click on CP and select CP_xxxxxxxxxx.tar.md5

(If you want to keep your data don't flash CSC).

-Click on CSC and select CSC_OMC_xxxxxxxxxx.tar.md5

-Click on USERDATA and select HOME_CSC_OMC_xxxxxxxxxx.tar.md5

When it finishes flashing it, it will automatically reboot and you can gain root access.

Optional: If you want to have the safety net passed (most of the banking apps use it), then you need to install the zip

as a Magisk module in Magisk https://github.com/kdrag0n/safetynet-fix/releases

How? Go to Magisk → Modules → install from storage and select the zip you downloaded.