columns with mixed data types

Create a 'Check Column' with 1900/01/01 for TBD.  Once created, now you can format this column as DATE format.

CheckColumn = IF(Table1[Due Date] = "TBD",DATE(1900,01,01),DATEVALUE(Table1[Due Date]))

Use this 2nd column to do the date checks and include logic to pull out the 1900/01/01.  ** Assuming you don't have any dates before 1899.

Text = IF(Table1[CheckColumn] > TODAY(), "In Progress", IF(Table1[CheckColumn] = Date(1900,01,01),"TBD","Complete"))

Paridhisharma

You can also replace the "TBD" with a specific date, say "2099-01-01", then change the column type to Date in Query Editor.