Is there a way to combine 2 field types together or maybe utilize a formula for this?

I want a whole column of cells to show different due dates and when the task is completed for single row/line, that specific cell can be changed to a ‘completed’ single select field while the rest of the column still shows their own respective due dates.

The only way I can think of this working is if I create multiple columns for a formula, within that formula it would show the due date in the target cell, I would have an if then function where if a checkbox is ticked, the target cell changes from due date to ‘completed’ text. This would require 3 columns however I have several items that require due dates. Is there a simpler or cleaner method?