How can I do x without the buffer scrolling horizontally to the end of the line?

[willfaught]

When it does that, I can't see the start of the next (shorter) line to decide whether to press x again to select it.

[tpm-cd]

Would Alt-; to pull the anchor to the start solve your use case?

If it helps, maybe a remap like

[keys.normal]
x = ["extend_line_below", "flip_selections"]

Note that this is not great, since repeated x will not scroll the text (the anchor will always stay at the beginning of the line where you first typed x).