I'm assuming you primarily use some mobile device, a smartphone or tablet. It may look differently on those devices.
I rarely use my mobile devices for casual browsing, generally feel too limited by the small screen, and AARP's huge lettering doesn't make it more pleasant for me. I like my large resolution PC display. However, I logged into my AARP account on an iPhone (with Firefox) and see the following:
This is the screen after one selects "All Rewards" on my iPhone. The new "Filter By" feature is the red bar. I believe It only shows if "All Rewards" is chosen ( @AARPCaroline@AARPTeri - is that a bug perhaps? ).
This is what it looks like on my iPhone when the red bar is tapped:
There, one can select one or more choices, and tap Apply.
Personally, I find it a bit more cumbersome than on a desktop or laptop, but the feature should be visible.
I hope this helps. If this feature is not showing for you, then please let the fine Beta programmers know.