The best way to search for all approved grants is to do so through Requests & Decisions. When you select the Appoved status it will auto populate all of the follow up categories as well. You may also want to put a check mark by the Closed status as well.
On the Dashboard the Approval bucket does contain approved grants, but when a follow up has been assigned to one of these grants the grant moves out of the Approval bucket and into the Follow Ups bucket.
If you aren't seeing all of your approved grants in the Approval bucket, try looking for them in the Follow Ups bucket.