I have also been playing with this, and believe I came up with a way to show the past 7 days only, dynamically based on the today’s date and journal-day values. Unfortunately, the query does not seem to update automatically yet (see discussion on https://github.com/logseq/logseq/issues/9802 )
Here is my version of the advanced query:
#+BEGIN_QUERY
{:title "Tasks completed in last 7 days"
:query [:find (pull ?b [*] )
:in $ ?start ?end
:where
[?b :block/properties ?properties]
[(get ?properties :completed) ?d]
[?p :page/journal? true]
[?p :page/journal-day ?dnum]
[?p :page/original-name ?jn]
[(>= ?dnum ?start)]
[(<= ?dnum ?end)]
[(contains? ?d ?jn)]
]
:inputs [:-7d :today]
}
#+END_QUERY