Confirming here, TFTPBOOT method works, I am on latest snapshot also with ax9000 international. With this, you dont even need to build your own image.
What I did, based on @Matezon's description:
Setup TinyPXE server at 192.168.1.100 (desktop), serving the openwrt-ipq807x-generic-xiaomi_ax9000-initramfs-uImage.itb (latest from Robi's repo)
UART connected, boot into u-boot
setenv ipaddr 192.168.1.1
setenv serverip 192.168.1.100
tftpboot 0x44000000 openwrt-ipq807x-generic-xiaomi_ax9000-initramfs-uImage.itb
bootm
Once Openwrt booted, SCP the sysupgrade package
sysupgrade -n /tmp/openwrt-ipq807x-generic-xiaomi_ax9000-squashfs-sysupgrade.bin
Now we should have openwrt booted with sysupgrade compat v 1.1
uci set system.@system[0].compat_version="1.0"
uci commit system
Sysupgrade to openwrt snapshot via LUCI
SSH or telnet again to install LUCI
opkg update
opkg install luci
This can be a good workaround untill the "international" version of packages are not built 