Got my FP6, the audio output isn’t great with the phone built in speaker. It might help if there were a equalizer built in. Using apps for this isn’t always very convenient and might not always work with every app, so this should be a build in feature.
I also use Wavelet, which seems to work fine. However, it would of course be better if there were something built into the software. Stock Android 16 does not appear to have a built-in equaliser. It seems that only Samsung offers an equaliser in the settings that is built into their launcher (AFAIK). Fairphone could add something similar to their launcher, but I doubt that will happen. So far, they have tried to stay close to stock Android.