I'm trying to make a formula that will find the maximum value in a column using the left function, but only for cells which contain a serial date value matching today's serial date value.

This is the formula (cell C1):

=LET(vBase;$A1:INDEX($A:$A;MATCH("ZZZ";A:$A));vLeft;LEFT(vBase;2);vRIGHT;RIGHT(vBase;5);vFiltered;FILTER(vLeft;vRIGHT=TEXT(TODAY();"0");"no such date");AGGREGATE(14;6;--vFiltered;1))

Might need to replace ; with , due to regional settings