Replace, ReplaceFirst, ReplaceChar and Regex_Replace in the cloud all have a limitation where arguments must be constants. Any attempt to use a column returns an error. This would a nice enhancement to have parity with Desktop. The below functions currently error out in cloud but work in desktop.
Replace(Column1,Column2, Column3)
Regex_Replace(Column1,Column2,Column3)
Could doesn't like that Column2 and Column3 are references to fields. It only works if you hardcode a string like "text". Desktop doesn't have this limitation.