https://www.undiscoveredscotland.co.uk/usfeatures/maltwhisky... seems to indicate that coke/oil is used these days, with peat being added if wanted for flavours.

I'm curious how historically the kilns would be fired across Scotland, if peat was more prevalent?

http://www.bairds-malt.co.uk/Bairds-Malt/Process/process mentions about using hot air.

https://www.laphroaig.com/en/whisky/our-process - Has some nice videos, including them using solely peat to kiln the malt.