It's because of the latest SuperWallpaperMars APK version => https://xiaomi.eu/community/threads/21-12-1.64111/post-638923
Workaround: Uninstall the SuperWallpaperMars APK then install this APK version =>...
Hello, try to flash an Official fastboot ROM via MiFlash Tool.
But if it doesn't work, the only solution to unbrick your device is to pay for a "EDL unbrick" service => The most known service is @*spam*paid*service* (Telegram). ;)
Mi Mix 4 device doesn't exist, the real/correct name is Mix 4. ;)
Two Stable ROMs by Xiaomi.eu are available so I don't understand your question... :)
EDIT: It's up to Xiaomi to release a new Stable ROM for this device. ^^
Hello, try this (enable the wanted app during step 6) => https://xiaomi.eu/community/threads/magisk-v23-0-breaks-safetynet-and-cts.63678/post-634170
;)