macOS has the prior keycombo for 'home' and 'end' occupied for other uses.
command + up/down arrow
Plus, the global key at bottom left fails for keyboard shortcut input when defining new binding for managing windowing rearrangement.
Your specific usecase has a native solve. Tap the status bar on any scrollable content view to scroll immediately to the top of the page. This has been around since, I believe, iPhone OS 1.
Tap? With your fingers?
Command+up arrow and down arrow behave exactly as you say on my computer: like home and end do on PC/Linux. Command left and right for how it also behaves on Linux/PC if you're in a text field. They always have? I use that combo all the time and only have issues in Safari tabs that overload the arrow keys with bullshit.
Command + up/down is pg up/pg dn. Command + left/right is home/end.