For the iodéOS upgrade see here, Unable to connect to my home WiFi connection - #2 by george
The XML is in this file, brax3/iode-7.2-20260131-brax3-spflash.zip · master · ota / release · GitLab , I don’t know whether it’s the same for Lunar.
Ubuntu Touch isn’t working well with the modem and has various other differences/difficulties, My Linux Phablet installed!
Be careful to understand completely the procedure before proceeding.
The firmware upgrade probably means to flash the vendor partition with the appropriate binaries.