There's me scrolling up and down and thinking "hey, it's not working!" But it's behind a flag on Firefox: https://caniuse.com/?search=view-timeline-name
It's been behind a flag for ages. Maybe because of performance issues?
Noticed the same thing. In Mac Safari it works without setting any flags.
For people saying it's not working in any browser - do you have some kind of reduced motion preference setting turned on? I can imagine that would have an effect on something like this and it's definitely working in Chrome for me.