This procedure works for me on a Xiaomi Redmi Note 9 Pro joyeuse.
The provider is Orange.

I can only assume that this will work for you too, but please be aware that you make these changes at your own risk.

Rom used to downgrad Android: joyeuse_global_images_V12.0.1.0.QJZMIXM_20201107.0000.00_10.0_global_eb964f842a
from https://xmfirmwareupdater.com/miui/joyeuse/stable/V12.0.1.0.QJZMIXM/ (the fastboot one)
than install of 20.04 Stable OTA-8 with ubports-installer_0.10.0_linux_x86_64.AppImage

Enable ssh connections
connect usb
enable developper mode
on PC 
adb push ~/.ssh/id_rsa.pub /home/phablet/
adb shell
mkdir /home/phablet/.ssh
chmod 700 /home/phablet/.ssh
cat /home/phablet/id_rsa.pub >> /home/phablet/.ssh/authorized_keys
chmod 600 /home/phablet/.ssh/authorized_keys
chown -R phablet:phablet /home/phablet/.ssh
sudo su
mount -o remount,rw /
apt update
apt-get install mc
edit /etc/ssh/ssh_config
remove the # before #  PasswordAuthentication yes

enable wifi and connect to your network

ssh connect
sudo su
mount -o remount,rw /
apt update
apt-get install ofono-binder-plugin-ext-qti
modified joyeuse.yaml in /opt/halium-overlay/etc/deviceinfo/devices
joyeuse:
    PrettyName: Redmi Note 9 Pro
    DeviceType: phone
    GridUnit: 21
    SupportedOrientations:
        - Portrait
        - Landscape
        - InvertedLandscape
    FlashlightSysfsPath:
        - /sys/class/leds/flashlight/brightness
    FlashlightSwitchPath:
        - /sys/class/leds/led:switch_0/brightness
    DoubleTapToWake:
        - /sys/touchpanel/double_tap|1|0
    MirAndroidPlatformClientEglFlush:
        - "!/usr/bin/unity8,!/usr/bin/lomiri,all"
    MirAndroidPlatformServerEglSync:
        - false
    MirAndroidPlatformServerPartialUpdates:
        - true
    LomiriInteractiveBlur:
        - true
    OfonoPlugin: binder
    OfonoImplementsIms: true
    
in /opt/halium-overlay/etc/ofono mkdir binder.d
cd binder.d
touch qti.conf
[Settings]
ExpectSlots = slot1,slot2
extPlugin = qti
radioInterface = 1.4

[slot1]
path = /ril_0
slot = 0

[slot2]
path = /ril_1
slot = 1

in /opt/halium-overlay/android/system/etc/init added init.disabled.rc 
# Copyright (C) 2020 - Dreemurrs Embedded
# These services are disabled due to them being unnecessary critical process
# and crash loop.

service lmkd lmkd_HYBRIS_DISABLED
    disabled
    oneshot
    override

# service vendor.imsdatadaemon imsdatadaemon_HYBRIS_DISABLED
#     disabled
#     oneshot
#     override

# service vendor.ims_rtp_daemon ims_rtp_daemon_HYBRIS_DISABLED
#     disabled
#     oneshot
#     override

service vendor.audio-hal-2-0 android.hardware.audio@2.0-service_HYBRIS_DISABLED
    disabled
    oneshot
    override

service time_daemon time_daemon_HYBRIS_DISABLED
    disabled
    oneshot
    override

# Disable console as it conflicts with the rootfs console
service console /system/bin/sh_HYBRIS_DISABLED
    disabled
    override

reboot

activate 2G/3G/4G/5G and VoLTE

plane mode then normal mode