Seeing how the old Derpibooru app and all of its forks are dead, I decided to take matters into my own hands and whip something up using Flutter. It also did me good as an exercise in learning that framework.
Functionality includes – Browsing images and videos – Search history – Share, copy link, download, open in browser – Add a tag to search, remove it, search it solo – Sleek design inspired by our favourite bug – Support for the API key to apply your set filters to the search results – Open source – LGPL3 license
The best solution is using the screen size to determine the best image to show. So if the screen size is 2560x1440, and you're trying to fit the image within a 600px box, you choose the medium previews instead of thumb. Here's a list of all the versions you can choose.