My users are required to complete a task every month and a list item is updated with a date when the task was last completed. I would like to send an email reminder to all users who did not complete the task for the current month. I want to use the Query List action to filter the list but I am not sure what would be the best approach?
I suggest you to create a site workflow. This site workflow can be scheduled to run once a month.
Use a "Query list" action to get all the IDs from the items of your list. Store the IDs inside a collection variable and use a "For each" action to loop through your IDs. Inside the loop you can then use another "Query list" and configure its filter to only get the values for the item where the item ID is your current ID in the loop.
To determine whether the entry in the items date column is in the current month, Use a "Calculate date" action. Get the the current date, substract 30 or 31 days and compare it to the fields value.
Get the user field who assigned to the task and send a notification .