The other day I wrote about a keyboard shortcut you can use to scroll in macOS apps. That key combo does work in Safari, but there is an additional combination you can use. Scrolling in Safari makes use of another set of keys.
[macOS: Use These Keys to Keyboard Scroll Through Apps]
Scrolling in Safari
You can use Fn or Option + Up/down arrow keys to scroll slowly. But in Safari, when you press the spacebar, it will scroll down one page at a time. And when you press Shift + Spacebar, it will scroll back up a page.
[Avoid Endless Scrolling: How to Quickly Return to the Top of a Page in iOS]