At most, i would expect the fan in the airfryer to spin faster, but i don't believe there is a relationship between frequency and power.
Resistive heating elements in airfryers should also be unaffected by frequency.
My guess is that heating element is tuned for 220v, but at 230v it goes to a much higher temperature? Or they suck at cooking :)
Edit: thinking more, a 20% faster fan could definitely be the issue.