Calc - cell navigation - keyboard keys stopped navigating the selected cell

LibreOffice Calc 7.3.6
Keyboard keys (arrows, page up/down) used to navigate the selected cell and the sheet.
When I pressed page down - it scrolled down both the sheet AND the selected cell.

Then it suddenly changed to a different navigation mode.
Keyboard keys (arrows, page up/down) navigate only the sheet, but do not navigate the selected cell.
Now when I press page down - it scrolls the sheet down, but the highlighted cell stays at the same position.
So now I have to use the mouse (in addition to the keyboard) - just to choose the selected cell.

How can I return back to the normal cell navigation - to move both the selected cell AND the sheet?

You may have turned off the scroll lock on your keyboard. Try this page:

Thank you for the advice!