Not a dumb question, no worries.
You can get a view of only projects in a given folder by clicking on the folder in the sidebar. Unfortunately, that won't hide those projects which do not have any available actions. To do that, you have to work a little harder.
One approach is to focus on that folder, then switch to context mode, and group by project. The view you get will be similar to but not identical to what you would see in project mode. You'll see a group for each project that has actions either available or remaining, depending on your choice of settings.
Another approach would be to install Rob Trew's excellent Where in OF
script. You could then do a search like "projects where (name of its folder contains <txt>) and (number of available tasks is not 0)" (the script will prompt you for the value of <txt>) and you'll see only projects in that folder with available tasks. It basically goes through your sidebar and clicks on all the projects that match that condition, then focuses on the result. It really is pretty darn cool :-)