I came here looking to add a request for this feature or up vote an existing request. Looks like I voted and commented way back in 2016.

What is strange about this missing feature is that on my trackpad, double-finger up and down zooms beautifully - smooth and responsive. Yet double-finger left and right does nothing (you'd expect it to scroll horizontally). If I use Ctrl + double-finger up and down, then the timeline does scroll, but it is not smooth. It kind of lurches left and right and feels laggy, unlike grabbing the scroll indicator and dragging it left and right, which is super smooth.

Agreed. I would like the horizontal scroll wheel to slide the timeline window left and right.

Update: Because you can use CTRL+Scroll to scroll the timeline, if you set your mouse configuration to Zoom on the thumb wheel (which is equivalent to CTRL+Scroll in a browser), you can scroll horizontally. This method works for me with the Logitech MX Master 3.

I also have a horizontal scroll (thumb) wheel on my mouse, in addition to the typical wheel between the buttons. Would be nice if it did something, like move forward/backward on the timeline. I'm ok with how the current wheel works but could see the advantage to having settings options to reassign what the wheels do and the direction they go.

I feel that the current scrolling is backwards.
If I CTRL+Scroll Up, I expect to go back in time. Not Forwards.

Please also put in an option to switch which way scroll wheel works.

Wow, for sure this would be useful. Since the screenshot feature dropped, I spend a lot more time zoomed-in so I can get a better look at what's going on. Being able to horizontal scroll using the mouse wheel would be so useful.

Note you can horizontally scroll by holding Ctrl and scrolling the wheel vertically.