I have a group of posts I want to create a dropdown filter using a custom field named categories, for example:
- History
- Activity
- Opportunity
I have a group of posts I want to create a dropdown filter using a custom field named categories, for example:
You would need to create a custom listview as a plugin and associated controller to do the custom filtering on the server. There's quite a lot of documentation about plugins and how to extend various elements of the Umbraco back-office here: https://our.umbraco.com/documentation/Extending/ but nothing specific to what you are wanting to do.
My suggestion would be to dig into the source code of Umbraco or a plugin such as MemberListView (https://github.com/YourITGroup/MemberListView) to see how it's done and use that as a starting point.