[Xiaomi Poco F3 / Xiaomi Mi 11X / Redmi K40] Immortal68:
Tried it like that and it worked perfectly. Caffeine keeps the screen & phone awake. The update takes about half an hour (rather add a few minutes than take a few) and then you're on the newest version.

For Magisk I'm still using the method described by @kwanice in this thread.

You need adb and fastboot installed, USB debugging over developer settings needs to be activated and the PC allowed to use it once the phone is connected.

Extract boot.img from the newest ROM-zip. I'm using the excellent tool Fastboot Enhanced by @xzr467706992 which allows you to add the ROM and then extract the boot.img by:

Download zip under "Assets" from here and extract it.

Start the GUI from FastbootEnhance.exe

Select tab Payload Dumper

Click Browse button and add the ROM-zip you installed on your phone

Select tab "Partitions"

Select boot (should be around 100 MB size), click the Extract Image button on the right and choose the location where to save the boot.img (ideally where your adb.exe is)

Start a cmd- or Powershell-window and locate your folder where adb and fastboot are installed through

cd C:/ADB/ (change accordingly. For me adb.exe is under C:/ADB/adb.exe)

Connect your phone to your computer and check that you're in the right folder with

adb devices

It should say:

* daemon not running; starting now at tcp:5037

* daemon started succesfully

List of devices attached

[some numbers] device

(if it says "unauthorised" instead of "device" you haven't authorised USB debugging on this PC - there should be a pop-up message on your phone about it)

Copy the boot.img to your phone with the command

adb push boot.img /sdcard/

If you put the boot.img somewhere other than in the same folder as your adb.exe you need to use the following

adb push X:/path-to-your-file/boot.img /sdcard/

If you did it correctly, the screen should read

boot.img: 1 file pushed, 0 skipped. [some numbers about speed]

Now open the magisk app on your phone, tap the "Install" next to Magisk, tap "Select and Patcha File" and select the boot.img you just copied to your internal memory (a file browser helps with navigating)

Tap "LET'S GO ->" and let the process work. It should tell you at the end, that the patched image has been saved in your Download folder, leave this screen open

in the command window on the PC type

adb pull /sdcard/Download/magisk_patched-23000_[some CODE]

The code is random.

Note: The magisk_patched part might change depending on version. Just have a look what it's called in the magisk app.

If you done it correctly the command window should show

/sdcard/Download/magisk_patched-23000_[some CODE].img: 1 file pulled, 0 skipped. [some numbers about speed]

Also, the file magisk_patched-23000_[some CODE].img should turn up in your ADB and fastboot-Folder.

Uninstall Magisk app

Reboot phone into fastboot mode

In fastboot check that everything works by typing into the command window

fastboot devices

which should show

[some numbers] fastboot

Now flash the modified boot.img with the command

fastboot flash boot_ab magisk_patched-23000_[some CODE]

It should show

Sending 'boot_ab' (12345KB) OKAY [ 1.234s]

Writing 'boot_ab' (bootloader) Partition boot_a flashed successfully

(bootloader) Partition boot_b flashed successfully

OKAY [ 1.234s]

Now restart the phone with

fastboot reboot

Once the phone is restarted, download the newest Magisk-app again and install it

Done!