How to create a view to display the last 6 month items in SharePoint list

Create or edit the view, then set the date column to “is greater than or equal to” [Today]-183 and, if future dates must be excluded, add an AND condition of “is less than or equal to” [Today]. This creates a rolling 183 day view that updates whenever the view is opened. SharePoint view filters support [Today] with day offsets, but not an exact calendar month calculation, so [Today]-183 is an approximation of six months. For large lists, index the date column and place that condition first to avoid List View Threshold issues. Use filtering to modify a SharePoint view | Microsoft Support

Have you tried a filter like this in your list view settings using "Created" or whatever date column and the dynamic [Today] option?

That might be easier to do through gear > List settings > Create view,  instead of from the "Add view" option in your list.