TWRP is NOT MANDATORY, not even needed to install Magisk
Although Magisk CAN be installed through TWRP (IF TWRP is available for the particular phone), by the Magisk Installation guide (available on Magisk Github- so many users use Magisk but do not date to ever open and read?!), the RECOMMENDED method (exactly because of the problem with custom recoveries for the new Android versions and new devices) to install Magisk is patching the boot.img and flashing
Hence:
- unzip Xiaomi.eu installation for your phone and extract boot.img file
- install Magisk APPLICATION, download from Magisk GitHub:
The Magic Mask for Android. Contribute to topjohnwu/Magisk development by creating an account on GitHub.
github.com
- by installing Magisk app, you are not rooted yet but you have the option to Install Magisk
- Take select and patch a file, navigate to and select your extracted boot.img, press Let's go
- Do not enable Recovery option (if it would be offered)
- Find the patched boot img file in Download folder, copy to PC, to your ADB/Fastboot folder
- Flash by:
fastboot flash boot <patched boot img>
Boot img must be from the actual Xiaomi.eu version you are running.
Upon updating Xiaomi.eu, you will need to repeat the patch and flash with the new boot.img
Btw, there is a guide and posts about here on XDA, about all this