Calendar formulas and conditional formatting

If you are using SEQUENCE() function in your workbook it means that at least you are using Excel 2021, please update your profile for us to give you the best solution.

My solution for you has been applied to every last line of your days calendar (Rows 24).

Formula:

=LET(ld,Year!B14,IF(MONTH(ld)=MONTH(B12),SEQUENCE(,EOMONTH(ld,0)-ld+1,ld)," "))

Rows 25

Formula:

=IFERROR(IF(B24=" ","",FILTER(TBlack[[Decription]:[Decription]],TBlack[[Black out dates]:[Black out dates]]=B24)),"")

Rows 26

Formula:

=IFERROR(FILTER(TBirthday[[Date]:[Date]],TBirthday[[Birthday this Year]:[Birthday this Year]]=B24),"")

And as you can see I transformed your tables into named tables, this means your formulas are easier to read and you don't need to adjust to the increase of new data.