Maps in both Apple maps and Kagi maps (beta) mode lack an indicator of scale. Estimating distances is one of the most common reasons I use maps so this feature is essential for me.
openstreetmap.org has scale indicator in the bottom left corner:
maps.google.com has scale indicator in the bottom right corner (clicking it changes units from meters to miles):
Both of these approaches would work fine, although I would consider placing the scale in the bottom middle rather than in the corner so it's easier to position the map such that the scale indicator is right next to the thing you want to measure.
Another option to cover my use case would be to implement an interactive tool to measure distances, but even then I think a scale indicator is something every map should have.