[sk546]

I'm sure Volvo recommend running at least 98ron petrol in the T8 engine, as the T6 is the same engine minus the Hydrid stuff, I'd be surprised if they don't recommend using the same in that too.
I only ever run my XC60 Polestar Engineered on either Tesco Momentum or Shell V-Power (less so V-Power at the moment as its price seems to be really high compared to other Premium petrol for no real reason).
Both fuels are 99ron and have decent additives & cleaners over standard 95ron petrol meaning injector and other fuel system components will remain in better condition for longer.
I havent done a standard fuel to Premium fuel back to back comparison in the XC60 so cant really say what difference there would be performance & economy wise but in my previous cars that I have done comparisons, there definitely have been noticeable differences.
With the T6 & T8 being small capacity engine utilising multiple methods of forced induction (both a supercharger and Turbocharger), it should react much better to higher octane fuel than more conventional petrol engines.