bonsoir Xavier,
There are various ways to obtain the result. The easiest is maybe that you go to this page and take all the values for the year 2021 (all dates, etc)
via a filter you check the month that relates to the week number
you could get an error message, this is a bug Coda is aware off and they plan to fix it.
If you want to generate a table like this it is rather easy. Create two tables as below and use the formula as given.
Sequence(thisRow.from,thisRow.to).FormulaMap(AddRow([alle dates in 2021],[alle dates in 2021].dates,CurrentValue,
[alle dates in 2021].weeknumber,CurrentValue.WeekNumber(),[alle dates in 2021].month,CurrentValue.Month()))
And of course this also could be done without the two tables, all in one table via a formula, but the approach above is visually speaking understandable if you get started with Coda.
cheers, Christiaan