How to group a list of dates to corresponding a specific weekday

have you thought of just applying a filter to columns B through D then filter on the day you want?

here is an alternative formula if you don't want to go with the filter
=IFERROR(INDEX(B:B,SMALL(IF($D$3:$D$41="Monday",ROW(D$3:$D$41)),ROWS($D$3:D3))),"")
it may be an array function (it isn't for me in my version) but if it doesn't work for you try activating it as an array so that {} appear on both ends, you do this by clicking on ctrl+shift+return at the same time while your cursor is in the function window. (You cannot add them, they have to appear when you press those three keys at the same time.)
oh, and based on your location you might need to swap the commas for semicolons.

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