On Apple website, why it loads that fast while all images are look sharp?

Question

Meanwhile, I’m struggling reducing images on my own website, but it just looks not clear enough compares to Apple and some others...

So what technique that is using in their website?

Answer 1

They may be going around TCP/IP overhead with websockets, async, QUIC protocol or similar; I can't verify ATM.

As design considerations more than coding, you could look over their media resources and their recommendations for seamless integration:

Marketing Resources and Identity Guidelines (+ product image downloads)
https://developer.apple.com/app-store/marketing/guidelines/#images
You should be noticing layout tips like "don't scale wrong..."

Human Interface Guidelines (for apps, but still has wisdom)
https://developer.apple.com/design/human-interface-guidelines/

And a braindump about handling all types of media and common mistakes on web, etc:
https://www.scantips.com/
This will probably reinforce Apple's guidelines AND be relevant to coding websites with media.

Answer 2

https://developer.apple.com/library/archive/documentation/NetworkingInternet/Conceptual/SafariImageDeliveryBestPractices/Introduction/Introduction.html