[Samsung Galaxy S21 Ultra] bANONYMOUS:
Did you just get your shiny new S21 Ultra? And the first thing you noticed is tons of preloaded carrier apps that can't be deleted? This is how to fix that.

Convert your phone into the one that would come from Samsung directly with a simple firmware flash!

BACK UP YOUR PHONE! ALL DATA WILL LIKELY BE WIPED!

You will need an SM-G998U/U1/W

Computer running Windows

USB-C Cable for your PC to Phone

This is only for SM-G998U/U1/W

Step 1:

Download the ROM of your choice. The firmware number does NOT need to match your phone, as long as you have an SM-G998U/U1/W

From each link, click the latest firmware in the list (what ever the top one is) and on the page that loads, click the blue button that says "Download from website"

(You can only download one in a 24 hour period so choose U1 or W wisely)

SM-G998U1 (U1 is unlocked, no carrier bloat, US radio bands)

SM-G998W (W is unlocked, no carrier bloat, Canadian radio bands)

The only main difference between the two is the Canadian W Firmware supports all radio bands aside from (n260, n261), the file size is a little bigger and will take up a fractionally larger amount of space on your phone as a result of also including all CSC's, but will allow your device to connect to any tower frequency with the correct SIM.

The U1 Firmware supports all US bands and works across all Canadian carriers, but does not have any Carrier CSC's as a result of the smaller file size.

Thanks to @milan03 for the info

Best measure is to use the W Firmware as it will be supported, but if you are positive of your carrier will work and bands are the same as US carriers, use the U1 to save some space.

Step 2:

Download Odin 3.14.4 and Samsung USB Drivers

Step 3:

Extract all of the .zip files that you have downloaded, and install the Samsung USB Driver

Step 4:

On your S21 Ultra, enter download mode by turning the phone completely off.

Once the phone is off, hold the volume up AND down at the same time, and without letting go of those buttons, plug a USB cable in from the computer to the phone

Do not let go of the volume buttons until the Download Mode screen is displayed.

Step 5:

Open Odin and make sure the S21 Ultra comes up as one of the COM ports

If it doesn't try rebooting your computer, and then connect your phone again

Step 6:

Click the BL Button, and select the BL file you extracted from the Firmware .zip

Click the AP Button, and select the AP file (This will take awhile, do not touch anything, don't even click your mouse or try to do anything else on your computer, it can crash, just wait, make a coffee or something, because depending on your computer specs, it can take up to 5 minutes to load that file

Click CP and add the CP file

Now this last part here, you have a choice, however I strongly recommend you do not choose the second option at this time, however you CAN, but you might face stability issues.

When clicking CSC, you can EITHER add the CSC file, which is what I recommend, OR you can add the HOME_CSC file.

The differences between these files is that the CSC file will wipe your phone, but this is recommended, because when you are switching firmware's from a different carrier build, which we are right now, you want to delete anything left over that could conflict with the new firmware being flashed, however, you CAN flash HOME_CSC which will keep all of your user data on the phone, but this could leave old firmware files behind that could cause stability issues with your phone, crashes, force close apps, or even boot loops.

It's recommended to ONLY use HOME_CSC when you are UPGRADING on the same build (eg, if you are on SM-G998W and UPGRADING to another SM-G998W firmware)

So if you are going from U/U1 to W, it's recommended to use CSC, if you are going from W to W, Home_CSC should be fine, if you are going from W to U1, you should use CSC.

Step 7:

Once you have made your choice of either CSC or HOME_CSC, you can now click Start and it will start flashing the new firmware.

This process will take a fair amount of time, go relax and enjoy that coffee you made while the AP file was loading.

Once the flash is done, it will say Pass in green, and your phone will reboot automatically into your new official carrier bloat free firmware.

If you picked CSC, you can now setup your phone just like a new phone and restore your backup, if you picked HOME_CSC, you should be at your lock screen, and the phone is ready to use.

Congratulation, you are now on the Official Samsung Firmware with no carrier bloat as if you bought the phone directly from Samsung.

Troubleshooting:

If you used CSC and the phone did not pass and says FAIL, try the flash again with HOME_CSC, once the flash passes, you should be back at the lock screen, go to settings, search for reset, and do a factory reset, wipe all data because something did not flash correctly the first time so you need to wipe the phone after the successful flash to guarantee no stability issues.

If you used HOME_CSC and the phone did not pass, use CSC and the phone will be wiped when it flashes, and you need to set up your phone like new and restore your backup during the setup screen.

If it still fails to flash both CSC and HOME_CSC, Download Mode probably timed out from your computer taking too long, at which point, you can try doing Step 6 BEFORE Step 5.

Turn your phone off completely, load all of the files into Odin, THEN enter Download Mode and immediately click Start to start the flash. This will give you a little more time for your computer to make the flash and hopefully download mode will not timeout, if it still fails, try a faster computer or a different/shorter USB cable.

If you are with Bell in Canada and you did not get the pre-order bundle promo E-voucher prompt from Samsung Members App, flashing the SM-G998W firmware linked above will fix this and you can redeem your e-voucher and get your headphones and smart tag.

This is a video I made on the S20 Ultra for flashing One UI 3.0 Beta/Stable, however the process is identical, just use the files from here instead of the ones linked in the video description

I will be replacing this video with a dedicated S21 tutorial once I have have finishing editing the new video, but for now this will give you an idea of how it works until 5:30 in the video, after that it's mostly related to One UI 3.0 Beta/Stable for the S20 so there's no need to watch further than that as the S21 would be done by that point in the video.