How can I change the # of lines the scroll wheel goes?

I cannot find a setting for it anywhere.

You can’t. In Plasma 6 only the Libinput driver is supported, and it doesn’t have this feature. In its place is a generic “scrolling speed” setting, which you can find in System Settings > Mouse & Touchpad.

For some background information:

Even with the old Evdev drivers which were supported on Plasma 5, scrolling never did go by number of lines; it was always a lie. Some apps may have actually done that, or respected the setting, but many did not, and apps also differed by what a line actually meant. Did one line mean a line of standard-sized text? Or did it actually mean one actual line height–even for, say, list views with 96px icons? One app may have done one thing; another app may have done another thing. So in practice the setting always acted as a “scale up or down the default scrolling speed” setting, so that’s what we have in Plasma 6.

Got it. Thanks.

I swear I saw a way to modify the scroll speed on the fly by pressing a keyboard modifier. So it’s normally at one speed but if I press ctrl + alt + e then it’ll scroll slower.

Am I crazy or is that a thing?