I think this is not so much related to the refresh-rate, even on 60Hz it feels terrible.

Enabling smooth viewport scrolling resolves the issue mostly, which means it is most likely caused that arrow key movements are not per pixels, but by a bunch of pixels at once. There are more places in OpenTTD that have similar issues, like news popping up.

Will need to look further into how arrow key movement works to see if this can be easily fixed, but possibly a simple fix is always applying smooth viewport scrolling for arrow key movement.

After looking into this in more detail, indeed, the best fix is to enable smooth-scrolling. I am currently applying some fixes to make smooth-scrolling a bit more smooth, but that is really the solution to this ticket. If you use arrow-keys, enable smooth-scrolling.

Initially I wanted to force enable it when using arrow-keys, but decided that would be weird; some people might not want it. So instead, I have made a suggested change to make smooth-scrolling the default.

PS: did you know that when you press SHIFT the arrow movement goes 5 times as fast? Easier to get to places :)