[Redmi Note 10S] RandomAccessVemuri:
By Following this guide, you

will

lose your warranty so keep that in mind before you begin. (Although you have probably already lost your warranty by unlocking the bootloader)

So, if like me, you ended up buying the Redmi Note 10S because it was very cheap (it's something like 200$ for a really good phone) and then just hopped on to xda forums for the latest roms and stuff, you'll find that not much development is going on regarding this phone, understandably because of "better" alternatives within the same line-up.

As a consequence, we don't yet have TWRP or CWM or any such custom recoveries built for this specific device (Redmi Note 10S) nor do I think they're coming any time soon, which is unfortunate since that would have made the process a tad bit more convenient. We don't have any custom roms built specifically for our device either (although we can probably use GSI roms)

So we'll now try to do the process ourselves.

Now, for the disclaimer:

DISCLAIMER

: I'm an amateur in terms of tinkering with android stuff and phones in general. The process mentioned below has worked on my phone but I would still recommend waiting for someone more....knowledgeable to weigh in his/her opinions. If you end up bricking your phone or if things go wrong, I'm not responsible, that's on you.

Also, please read the entire guide first and then begin.

Alright, with the appetizers out of the way, let's just crack on to the main course:

STEP-0: Requirements:

Redmi Note 10S

Install OEM fastboot drivers

Obtain android platform-tools along with knowledge about how to use it

Your Bootloader should be unlocked (wait for 1 week after first attempt at unlocking after which you'll receive your "permission")

Fastboot rom from here

Magisk apk

Being ready to lose your data (in short, don't personalize your phone just yet (....and also take a backup of everything)) and accept that you'll have SafetyNet related issues until you do some other special stuff

Enable Developer mode and USB debugging

STEP-1: Obtain boot.img (and vbmeta.img)

What we need is a boot.img that we can patch using magisk. We can do some code-fu to pull it from the phone but we don't need to do that. We can instead obtain the fastboot rom from here (I don't think region matters but take accordingly just to stay safe). While downloading, you'll see that what you're downloading a zip. This is intended because the boot.img (and the vbmeta.img) is within this zip file.

Anyways, once you download it, unzip all of the contents into a folder and move on to the next step.

STEP-2: Patch the obtained boot.img:

Take the boot.img from the zip file you obtained earlier and move it into the internal storage of your phone. Install the Magisk Manager apk from here. Install the apk and then after opening, go straight to installing Magisk, then select "Select and Patch a File" and then select the boot.img that you moved into the internal storage. It will then start patching the boot.img after which it will generate a patched boot.img, the directory of which is mentioned at the end of the patching process.

Move the patched boot.img back into your computer and move on to the next step.

STEP-3: Flash the patched boot.img:

Alright, this is the final leg of the journey (or should I say, desserts?).

Keep the vbmeta.img and the patched boot.img handy as you will be needing them here. You can find the vbmeta.img in the zip file you extracted earlier in the guide.

NOTE: The vbmeta.img is especially important because if you don't flash this while disabling verity and verification, you'll be stuck in a bootloop until you flash the stock boot.img (the boot.img before you patched it) back because this.

Alright, with all of that at hand, boot your phone into fastboot mode.

Now disable what is equivalent to the windows version of secure boot:

fastboot.exe --disable-verity --disable-verification flash vbmeta vbmeta.img

And then the following command that will finish it off:

fastboot.exe flash boot patched_boot.img

If you get stuck in a bootloop (perhaps because incorrectly flashing vbmeta.img or anything else), flash the stock boot.img with the same command and try the process again

And then finally for the cherry on top:

fastboot.exe reboot

After all that is done, hopefully you will see the setup for MIUI. Complete it as you normally would, and after the setup, you will find the magisk manager preinstalled but it will have the placeholder android app logo. Open that and it will prompt you to complete the download and installation of magisk manager. Do that and then open magisk manager (at this point it will have the familiar logo), go straight to installing Magisk and then select Direct Install (Recommended) and then let it do its thing.

After that, it will prompt you to restart your device to complete some stuff at which point you have successfully rooted your phone.

Aftermath:

I would like to remind you that SafetyNet will fail, even if you enable MagiskHide. You will have to do some other stuff to fix that if you want to use stuff like Google Pay so if that is a deal breaker, I suggest you don't follow this guide yet until some recommendations regarding SafetyNet pop up in this thread (or if you find some stuff elsewhere (please do let me know)).

Weirdly the Widevine rating is still at L1 according to DRM Info so I guess Netflix and other stuff will work fine(?). I don't use netflix or prime video so I can't help you there.

Concluding:

If there is anything step I have missed out or some issues you're facing, please let me know within this thread. I'll be happy to resolve the issue. If there are any recommendations regarding SafetyNet or any recommendations in general, I'll be happy to listen.

EDIT 1: You can't use Netflix because you won't be able to find it in Google Play Store.

EDIT 2: You can use Netflix and other DRM protected applications by installing the following Magisk Modules:

Riru (This is required by the next one)

Universal SafetyNet Fix (To pass SafetyNet ctsProfile evaluation)

MagiskHide Props Config (!!MOST IMPORTANT!!) (To get fingerprint certificates and pass other authentication related stuff)

Of course, as is with software, this stuff may eventually be patched by google or netflix so you should still refrain from using this guide (or rooting in general) if you don't want to deal with the hiccups down the road.

Certification is still L1 (weirdly) after installation of the modules and you will now be able to find Netflix in the store.

EDIT 3: Edited the guide after @murigny64 's reply (Thanks!)