Reprex:

waldo::compare(as.Date("2021-08-17"), as.Date("2021-08-16"))
#> `old`: 18856
#> `new`: 18855

^{Created on 2021-08-17 by the reprex package (v2.0.0.9000)}

I understand this is difficult because dates might be stored as a large variety of formats but the current behaviour makes it difficult to read the output.

I believe a slightly better behaviour would be to display dates in the same format used by print.Date(), i.e. "%Y-%m-%d". But you might have a better idea.