what is an efficient way to specify multiple columns in a groupby with streaming window operations?

You are mixing strings with a column in the groupBy. The window window($"EVENT_TIME", "60 minutes") is correctly interpreted as a column but the list of column names needs to be columns to match, it’s not possible to mix types.

What you can do is:

val cols = groupCols.map(col) ++ Seq(window($"EVENT_TIME", "60 minutes"))
val aggDFrame = dframe.groupBy(cols: _*).agg(...)