I suppose you want to use "datetrunc".
will bring the date of last Monday.
So, to get "5" with using this,
I mean the formula "weekday" will not change by changing the property..
Aha I thought the start of the week would change how numbers map to weekdays (i.e. Monday week start -> weekday #1 = Monday)
You are very welcome.
And if you don't mind, could you mark my answer as "correct"