I notice that there is a search box at the top of the window, but then also the "Search Cards" function in the menu. Trello seems to lean more heavily towards using the top-bar search text field, having the "/" keyboard shortcut. However, I fund it of very little-use the way it just brings the results up in a list below the search box, and the way it shows the actual cards, which takes up a huge amount of space, showing very few results without expanding and a lot of scrolling. I can't see any way to then extend that search to a board filter, the same as the other "Search Cards" function.
I can see why there is the top-menu search, because it's across all of Trello, not just the current board. But I find the "Search Cards" function far more useful and wish it was somehow more visible and had more emphasis than the top-menu search field.
I'm also not sure why "Search Cards" is hidden in the menu. It's the most critical feature from my perspective and having the extra click and slide of the menu adds a lot of extra clicks.