Hey Alice,
Thank you for this, however, I don't know how to make this work with what I'm doing. (sorry, newbie!)
I have the flow running on a recurrence, once per hour.

The ODATA query is in Get items 2 to see if the user exists, and then I use the following true/false condition to decide what to do with them:
@equals(length(body('Get_items_2')?['value']), 0)
I tried to drop in the filter array between the Get items 2 and the condition and then play with the condition statement, but I couldn't get it to work.