The rectangle means it is a non printable character and is not in your font set of characters. I would start with searching the origin of data because removing characters means you change the data. On your capture I saw 0 to 2 rectangles and maybe there are more, even in middle of a variable; Those can be different characters, not neccessary the same one; in case you recognize specific hexa characters you can replace then to any character(s) you chose using TRANSLATE function: ne_var = translate(old_var, new_chars, old_chars); new_chars and old_chars should fit by order.
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