Hello!
According to this guide, since EMUI 9+ the recovery_ramdisk parition will be used for magisk payload.
1) Download your current firmware with huawei firmware finder
2) Extract the UPDATE.APP from the update.zip file downloaded by firmwarefinder
3) Extract recovery_ramdisk.img from the UPDATE.APP (for me it was called "recovery_ramdis.img)
4) Transfer the ramdisk image to your phone by any means
5) In magisk choose "Install"->"Install"(again)->"Select and Patch a File"->[Now choose the recovery_ramdisk.img]
6) Magisk should now integrate the magisk payload into your recovery_ramdisk.img and will produce a new file called "magisk_patched,img" located in your /storage/emulated/0/Download directory
7) Get the patched.img via "adb pull /storage/emulated/0/Download/magisk_patched.img"
8) Restart your device in fastboot mode. Unfortunately button press events are not captured properly at the moment so you might try "adb reboot bootlaoder" command
9) Execute "fastboot flash recovery_ramdisk magisk_patched.img"
???
10)Profit
edit2: Unfortunately booting's a bit ****y now.. Whereas you used to boot by just simply pressing the power btn (from power off state) and acknowledging that your phone is now oH sO vErY unseCUre PLS UnDo kThX, you now HAVE to press vol up+power btn until you see the first "huawei" flash image.. After that release every button. Your phone should now show you the "oMg SO scARy unloCk" screen, however it should now just say "your device is now booting" instead of giving you 3 options and making you wait 5 seconds.. Rebooting is a bit **** now but since it no longer gives you those 5 seconds wait time, i see this as an absolute win

)
edit3: don't worry, be happy. After testing, i can report that this works for me. You may take my recovery_ramdisk.img. I used this based on the 261080 build (based on android 9.1). I am in the C432 region (Western Europe, France). I am uncertain if this works internationally, so you might not want to use this if you are outside this region. Otherwise feel free to!
Big Download link to recovery_ramdisk