A nice workaround might be modifiers with the page keys, for ex. Shift + Page Up/Down to scroll half-pages or full pages on the main view.

As an example, the yazi file manager works this way, using by default J and K (capital 'j' and 'k') to scroll through the preview pane. And I was able to customize my bindings for yazi in ~/.config/yazi/keymap.toml:

[manager]

prepend_keymap = [
  { on = "<S-PageUp>"  , run = "seek -5", desc = "Preview up 5" },
  { on = "<S-PageDown>", run = "seek 5" , desc = "Preview dn 5" }
]

The shift+pgdown / shift+pageup was what I was thinking too.

Would that be simpler than the "proper" way you've described, Stefan? If it's do-able, it would probably be good enough for most people. Scrolling one line at a time is often tedious.