What I'm still missing is a custom #recovery that can actually do any useful stuff (especially full #backup).
My device has recovery as a #ramdisk in vendor_boot, and there are some prebuilt vendor_boot images with #twrp around, which I don't want to use directly because there's also an init-boot ramdisk in there that needs patching for root with #magisk ... and as far as I understood now, these ramdisks are userland only, using the shared #kernel from the boot partition, so it's unlikely a recovery built for #HyperOS1 (#Android 14, #Linux 5) will work with #HyperOS2 (Android 15, Linux 6).
What I *did* try nevertheless was modifying my vendor_boot using Magisk's #magiskboot utility, replacing ONLY the recovery ramdisk. It resulted in #bootloop trying to boot the normal system, so there seems to be something I still don't understand (I *thought* this ramdisk would only ever be loaded when booting to recovery).
For now, I'll live with the useless stock #Xiaomi recovery. Attempting to do my own build of twrp or orangefox really is too much hassle 