Also broken for me:

Safari 18.0 (20619.1.26.31.6), macOS Sequoia 15.0

Me too. Thumbnails just appear black.

Safari 17.6 (19618.3.11.11.5), MacOS Sonoma 14.7.3 (23H417)

It works on Chrome on the same machine.

Works fine on macOS Sequoia 15.4 with Safari 18.4.

Worked for me in Mobile Safari in iOS on my iPhone.

Maybe it’s iOS version dependant. I’m a bit out of date (on purpose for jailbreak) and the demo is broken for me.

I'm up to date and it's broken for me :/

Same setup, didn't work. (Empty space where blur supposed to be.)