I just purchased Affinity Photo as a possible replacement for a slightly old Photoshop Elements I have used for many years and I was doing one of the most common tasks I use PS for, tidying up old digitized documents (such as census documents, out of copyright books, etc.). These often have that sepia, aged paper, background and the black text is not usually black. I was searching through Affinity for a black and white levels tool similar to what is in PS with those white, black and grey eye droppers that allow you to quickly select and decide what you want as white, and you can zoom into the scanned text to pixel level if you choose and decide what you want to be black. You cannot achieve this using only black and white sliders (nor white balance) because the PS levels function, using the eye droppers, adjusts a number of different elements when you use the levels tool in the manner I do. From this particular thread, and from reading several others in this forum, I conclude that the reason I cannot find a way to do black/white levels in Affinity (at least yet) the way it can be done in PS is that those functions are not in the program. Affinity is a complex program but is the eye dropper levels function really that hard to implement because I would think that type of tool is a very useful and commonly used one, even when tweaking digital photos.
