I'm sorry but... wifi backup does not need cable.
Just the wifi backup is broken, with cable it works fine.
I made the backup with wifi on two iphone before updating to ios 26.4 and was fine.
The phones are different, different apple account, different windows machine, i tried with itunes, the itunes from the microsoft store and Apple Devices from the microsoft store.
I have already reset privacy settings and network settings (loosing all the wifi passwords because keychain is... Magic) and nothing work.
Reinstalled itunes, made a clean installation of it, reinstalled the bonjour service, nothing.
With the same machine i can backup correctly via wifi other phones with ios 26.3.1 and earlier.
The os is windows 11.
I already know what support will tell me to do: reset the two phones default without restoring backup because this will magical fix everything :(