Populating columns with days based on a selection-CodePudding

I am trying to build a sleep tracker in Google Sheets (

Then, repeat the sequence in both rows starting in C2 and C3:

=SEQUENCE(1,DAY(EOMONTH(A2,0)),A2)

But formatting row 3 as ddd:

PS: yes, you can do row 3 with TEXT and INDEX. Choose your preferred one:

=INDEX(TEXT(SEQUENCE(1,DAY(EOMONTH(A2,0)),A2),"dddd"))

UPDATE with TEXT VALUES

Return to your previous A2 dropdown and try this, using MATCH to find the number of the month, and DATE to locate the correct beginning of the month in that year:

For row 2:

    =SEQUENCE(1,DAY(EOMONTH(DATE(A1,MATCH(A2,{"January","February","March","April","May","June","July","September","October","November","December"},0),1),0)),
DATE(A1,MATCH(A2,{"January","February","March","April","May","June","July","September","October","November","December"},0),1))

For row 3:

=INDEX(TEXT(SEQUENCE(1,DAY(EOMONTH(DATE(A1,MATCH(A2,{"January","February","March","April","May","June","July","September","October","November","December"},0),1),0)),
DATE(A1,MATCH(A2,{"January","February","March","April","May","June","July","September","October","November","December"},0),1)),"dddd")

)