Annotating graph with events

The information you have provided is not making the problem clear to me.

But if you date table is at date level and you trying to join the data to MMM-YYYY column from another table which data in MMM-YYYY format, that will create Many to Many. Better would be

Create date in another table

Date = "01-" & Table[Month Year] // Only if it is in MMM-YYYY format.

Change data type of this as date. And Join using This new date to date table

Sure, you could do something like the following. Obviously I do not know your tables and code but hopefully this gets the idea across.

ToolTip Measure = 
VAR __Date = MAX('Date Table'[Date])
RETURN
  CONCANTENATEX(
    FILTER(
      'Events',
      [EventDate] = __Date
    ),
    [Description],
    ","
  )
      

Tried both proposed solutions but neither worked.

The events table that I have is an excel spreadsheet with 2 main columns: Event Date and Event.

I want to be able to hover over or click on a given month/year in the graph and have some annotation in the tooltips.

Here's the date table I have:

And here's the events table:

If I were to select/hover over the spike in the orange line right before 2018 (which would be Dec 2017), I want the tooltips to display "Dim Screen"