Currently, the "Find tickets" search bar is hidden by default, and you must click on the icon (looks like a Q or a magnifying glass) to reveal it. This seems strange to me, because it discourages users from using the search functionality. The most obvious effect is that it takes an unneccessary extra step to access search. But the more serious effect is that it makes it much more difficult to locate the search bar at all!

My eyes (and those of many other web users) are trained to visually seek out a white search box, usually in the upper right corner of the page. The current design thwarts this. Instead of finding the search box, our eyes are drawn to the "Go to a project" box, which is, confusingly, dressed up to look like it should be a search bar, but is actually a drop-down list. Even after having used Lighthouse for over a year, and being well aware of where the search bar is and how to access it, I always instinctively aim for the "Go to a project" box first, then stop and stare at it in confusion before my brain kicks in and says "Oh, right, the search bar is hidden over there by that icon."

So, I think that it would significantly improve the usability of Lighthouse if the ticket search bar were revealed by default, perhaps taking the place of the icon, or else made larger and more prominent, and placed above the "Create new ticket" button at the top of the right-hand sidebar. I also strongly recommend styling the "Go to a project" box to make that element look less like a search bar.