How to make a table of weekdays and amount of corresponding daily notes?

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2

Try this:

TABLE WITHOUT ID weekday , length(rows) as count
FROM "<your-folder>"
GROUP BY dateformat(date , "E cccc") as weekday

If Obsidian recognises your date format as a valid date, it should work out of the box. If not change the last line to

group by GROUP BY dateformat(date(date, "yyyy-mm-dd"), "E cccc") as weekday