@josedimaculangan - just so you understand the "why" of it (or in case someone else looks at this exchange); the curly brackets are used for named ranges, typically across sheets. Square brackets and the colon are used for ranges in the same sheet you are working in, with the left side of the colon being the start and the right side being the end. When both sides are just the name of the column, it applies to the whole column.

You may have seen formulas written similarly with NO brackets but with the colon - when the column name doesn't have any numbers or spaces or special characters, you can skip the brackets entirely, but they never hurt anything to add in.

@josedimaculangan Excellent - I just noticed that you asked it (and your image is coming through as broken).

For what it is worth, two different countifs() is what I'd have gone for there (countifs(everything plus complete)/countifs(everything EXCEPT complete), plus an error trap at the beginning to prevent a divide-by-zero error (iferror(formula,"")).