Hello @Lorraine_Becker!
When you use filter or lookups, you always have to compare info with the same type of data, what I mean is, in you case you want to compare 2 dates but you are comparing a list of dates with Currecy that’s why it doesn’t work. If you want to know more about these icons check this article.
First things first, why your Month Trade Closed is a list of date?
Well, I suppose you made a filter to get this value. If my assumption is correct then, when you make a filter you always get a list of values, even if it just found one, you get the icon that is a list of values. How do you fix this? you put something like a .First() at the end of the filter
Table.Filter(X=thisRow.X).First()
Now you are telling it to the filter that you only want the first you find, this way you now have one date instead of a list of dates.
There are some cases that you actually have a list of dates on propose. In this case you could use contains(), containsOnly() or containsAll() formulas to help.
Another thing you have to be careful is, when you select a column as a date, and you only show for example the month (I supposed is what you did in thisRow.Month) the complete date is still stored in the column even if it only shows the month.
So whenever you want to know if a date is inside a range of dates you will have to provide either a Start date and an End date and use filter like this
Table.filter(Date>=thisRow.[Start Date] and Date<=thisRow.[End Date])
or compare the month values of the dates as it is in your case.
[Trade Closed (Date)].Month() = thisRow.[Date column].Month()
Now you are converting these dates to numbers with the help of the month() formula so now you could know if both dates are from the same month.
You have to be careful though, if two dates fall in the same month but in different years your filter will also select these.
Filters can bit a bit tricky, but when you understand how they work you feel like you have superpowers