Well, at least we have overcome the first obstacle ... since the
formula now seems to work ...
As you requested it, the formula is intended to return the Last cell
address thanks to the MAX() function ...

It could be that using <=K6 creates some illogical pattern with your
data ...

My initial recommendation for you is to test the formula without
<=K6 ... but with =K6 to fully master the formula, and determine if
you are reaching your objective.

Should you still face difficulties, feel free to send me your
spreadsheet ...

HTH