PowerBI custom filter

jgrima ,Ensure you have a date table that includes columns for Year, Month, and Date. If you don't have one, you can create it using DAX.

In your date table, add a custom column to identify the previous year's December for each year. You can use the following DAX formula:

PreviousDecember = IF(MONTH([Date]) = 12, YEAR([Date]), YEAR([Date]) - 1)

Add a slicer to your report and set it to filter by the Year column from your date table.
Create a Measure for Filtering:

Create a measure that will be used to filter the table based on the selected year and the previous year's December. You can use the following DAX formula:

FilterMeasure =
VAR SelectedYear = SELECTEDVALUE('DateTable'[Year])
RETURN
IF(
YEAR('YourTable'[Date]) = SelectedYear ||
(YEAR('YourTable'[Date]) = SelectedYear - 1 && MONTH('YourTable'[Date]) = 12),
1,
0

Apply the Measure as a Visual Level Filter:
Add your table visual to the report.
Drag the FilterMeasure to the Filters pane for the table visual.
Set the filter to show only values where FilterMeasure is 1.