Quick and possibly dirty solution to update your massive Zigbee network's devices.
git clone https://github.com/fabicodes/zigbee2mqtt_ota_updater.git
cd zigbee2mqtt_ota_updater
pip install -r requirements.txt
Edit the following options in the main.py
MQTT_SERVER = "hostname/ip" # Hostname/IP of the MQTT Server
MQTT_PORT = 1883 # MQTT Port
MQTT_USE_AUTH = True # Use username + password authentification
MQTT_USER = "user" # Username for authentification
MQTT_PASSWORD = "password" # Password for authentification
MAX_CONCURRENT_UPDATES = 1 # Number of concurrent updates it should do
python main.py
And wait. It can be always restarted, even while an update is running.