I think its an EU safety directive. They just treat us all like children, its my pet hate on my Honda Jazz. I drove a Peugeot 108 last year and it did not have warning.
I don't think it's EU mandated - at least not the way Honda have done it. My 2020 Corolla displays a warning but it removes it after a few seconds without me having to do anything.
Unfortunately it's not all sweetness and light because the infotainment unit won't automatically start playing from my iPod Touch when I turn the engine on. In fact the audio function has to be switched back on and
then I have to select the correct source. That's better than what my Jazz did when I first got it but still irritating. Possibly it's Toyota's rubbish attempt to fix a long standing issue where some owners complained that the infotainment unit randomly started playing music from their iPhones. Perhaps the fix was simply to disable iFunctionality on start up.
Hey ho