FIRSTNONBLANK, LASTNONBLANK, FIRSTNONBLANKVALUE, LASTNONBLANKVALUE – DAX Guide
FIRSTNONBLANK: Returns the first value in the column for which the expression has a non blank value.
https://dax.guide/firstnonblank/
LASTNONBLANK: Returns the last value in the column for which the expression has a non blank value.
https://dax.guide/lastnonblank/
FIRSTNONBLANKVALUE: Returns the first non blank value of the expression that evaluated for the column.
https://dax.guide/firstnonblankvalue/
LASTNONBLANKVALUE: Returns the last non blank value of the expression that evaluated for the column.
https://dax.guide/lastnonblankvalue/