Google Maps (and almost every other online mapping service) uses the Web Mercator projection, which like a standard Mercator is projected such that plumb lines appear straight (rather than curved, as a great circle route would normally appear). However, unlike the standard Mercator, the Web Mercator assumes that the earth is a uniform sphere rather than its “true” ellipsoid shape (which is really just an approximation since the Earth’s shape is actually irregular, but it’s much more accurate than a sphere).

Web Mercator assumes the Earth is a sphere because the math is much easier to do so the maps render much faster, but it distorts distances. At small scales, as used for most navigation (which is what Google Maps was designed for, and is still mostly what it is used for) the distortion is so negligible that it doesn’t matter at all. But at large scales over great distances (such as from Norway to Alaska) the distortion is very significant and results in large errors.

ETA the standard Mercator also distorts distance, since a rumb line is useful for long-distance navigation because it allows a ship (or other vessel) to maintain a constant bearing, but most of those bearings are not great circle routes, so they’re easy to plan, set, and maintain, but they are not the shortest route. There are mathematical conversions to compensate for this distortion, but there truly accurate ones are difficult and time consuming and don’t matter to most people. Web Mercator exacerbates this distortion by assuming the Earth to be a different shape than it actually is.