A block doesn’t have an attribute :block/journal-day, there is no relationship between the two.
Can only accomplish with more advanced tinkering.
I’m off to bed now, but you can find an example here: https://siferiax.github.io/#/page/66265648-109a-4321-a6f4-75c3ea4c3310
something similar is used in this topic:
And also yes, when clicking on the column header it will always sort by literal (ie column visible value) and not underlining data.