9900k likely doesn't work because they're not up yet. Other CPUs (and in general products) do work:

https://www.amazon.com/Intel-i7-8700K-Desktop-Processor-Unlocked/dp/B07598VZR8/ https://www.amazon.de/Intel-i7-8700K-Desktop-Processor-Unlocked/dp/B07598VZR8/ https://www.amazon.co.uk/Intel-i7-8700K-Desktop-Processor-Unlocked/dp/B07598VZR8/

https://www.amazon.com/AMD-Ryzen-Processor-Wraith-Cooler/dp/B07B428M7F/ https://www.amazon.de/AMD-Ryzen-Processor-Wraith-Cooler/dp/B07B428M7F/ https://www.amazon.co.uk/AMD-Ryzen-Processor-Wraith-Cooler/dp/B07B428M7F/