Replace and Substitute will both swap out cell content, but they do it differently. The Substitute function will find content you search for, and the Replace function will count characters. Sometimes you want one method and sometimes you want the other. This video shows how they both work:
Excel formula: convert Roman numerals to regular Arabic numbers
Last year, I did a TikTok video blog post about Excel’s =ROMAN function (watch it here). It will convert any regular Arabic number to Roman.