The boot.img to patch must be the same as the rom you are using.
Try renaming magisk.apk and magisk.zip and flashing it with Twrp. (You may need to flash vbmeta and use "fastboot flash --disable-verity --disable-verification vbmeta images\vbmeta.img").
Yeah, I downloaded the correct ROM (miui_SURYAEEAGlobal_V220.127.116.11.RJGEUXM_0deb1eaf6f_11.0.zip) and extracted the boot.img from that.
Renaming magisk.apk to magisk.zip and flashing it just installs the app doesn't it, it doesn't root the phone as far as I'm aware.
I followed the instructions here, which say that you should only tick the "Patch vbmeta in boot image”
option when patching the boot.img in Magisk if the device does NOT have a separate vbmeta partition. The Poco X3 does have a separate vbmeta partition,, so I didn't tick that option.
The Magic Mask for Android
I've tried the "fastboot flash --disable-verity --disable-verification vbmeta vbmeta.img" command with four different versions of fastboot that I've got, dating from 2016 to 2020, and they all reject the "--disable" switches as an "unknown option".
I tried it without those options, so I flashed the patched boot.img and then did "fastboot flash vbmeta vbmeta.img" but after rebooting Magisk still shows that root is not installed.