Currently investigating what is described here:
SMS Backup & Restore stops working when upgrading to Android 14 due to sub_id value errors. Fix by editing the backup XML file to change all sub_id
pupuweb.com
First, I tried: sub_id="-1" (after restoring and changeing standard app back to google messages, messages showed some grey and empty messages flickering, I assumed this would be a loading screen, but after waiting long time this still did not work). Then, I tried sub_id="1", but still no luck.
I also sent one SMS after restoring of the manipulated xml file. Still no success, I did not even receive the SMS, although I am connected to mobile services and phone calls do work.
When restoring from the xml file, it was necessary to make "SMS Backup&Restore" the standard App (Settings -> Apps -> Apps verwalten -> three dots menu top right: Standard-Apps -> Messages: "SMS Backup & Restore") because the in-App change did not work (screen loop).
I also deleted google messages cache and data (Apps -> Apps verwalten -> Messages -> Delete data and cache) before restoring the xml file.
Also I copied the xml file locally from my PC (PC\POCO X4 Pro 5G\Interner Speicher\Android\data\com.riteshsahu.SMSBackupRestore\files) because in google drive, the edited xml file was not shown. After copying, I needed to reboot the X4 (more than once) before they would show up in the menu.
At this time, I am not really sure, if I have to also change the SIM card (to which mobile number all the SMS belong to) of my old phone to the new one (X4), before the SMS show up. Google messages help says, that the messages are not connected to the google profile and still belong to the phone number (SIM). So I swapped the SIM (after restoring the sub_id='1'). No success. So I restored again, deleted google messages cache and data, started messages. It was the showing again five grey messages, just like purely grey icons that were all flashing from black to grey at the same time like a loading animation. I have ca. 700 SMS in that xml file and I am currently still waiting...
This has gone ridiculous already, I think I will start a new thread with a better title and hope for help.