As I may have mentioned, I'm primarily a desktop user, and I find SoundSource on macOS to be really excellent at EQ. It's about US$40 or so, but totally worth it. You can EQ any app that produces sound on your mac with 0 restrictions.What software do you use to EQ your IEMs? I haven't found anything great for my DAPs. The only parametric EQ I"ve had luck with is Equalizer APO, but then I need to get my laptop invovled. I've tried Wavelet, but it didn't work well.
I also like the fine control over each app's sound output destination and volume level. For eg, I'm on Zoom/Teams meetings at least 3 hours every day, and it is pretty great to be able to mix in 'background' music out through the BF2. Like if I need Jim Morrison to drown out some boring presentation.
Doubt Apple will ever allow system-wide EQ outside of the very limited control provided for their own Music app. Their default assumption is that if you have iOS, you should be using their Music anyway, and discourage use of anyone else. If you want to EQ Apple Music on a portable device, use Android instead.but I think IOS might not allow systemwide EQ control to an App.