Good question, because the GUI isn’t intuitive here. The Quality drop-down is a permanent part of the user interface, meaning it’s visible whether it is relevant to the codec or not.
For instance, HuffYUV and Ut Video are lossless codecs, so there is no concept of Quality at all. Those codecs capture everything by design, but the Quality drop-down is still there even though it does nothing.
Same for ProRes. The Quality drop-down does nothing. Encoding quality is configured by the vprofile option in the Export tab > Other box. The link below is a useful description of the five profiles available. Profiles 0 and 1 are not visually lossless; they are designed to be lower quality for lower disk usage, but still be ProRes format for editors that need it. Profiles 2 through 5 are visually lossless, with 2 being normal, 3 being for the paranoid (you may as well go true lossless at this point), and 4 if you need 4:4:4 colorspace.