I need a fix to select only the 4 right digits in cells that are not
empty in a column (Range J2:??)

I'm not entirely clear on the meaning of "fix" and "select" as you used them
in your question. This formula...

=RIGHT(J2,4)

will return up to the right-most 4 characters (that is, from zero to four
characters depending on the cell's content) in a cell (J2 for the above
example usage) and can be copied down to handle the other cells in the
column. Is that what you are looking for?

Rick