akd77
I don't remember there being a system wide EQ, someone please correct me if I am wrong.
Some music streaming apps include EQ, but obviously it only works within that app.
As for what possibilities are within the software.
GrapheneOS is a bit like "standard" android, with an additional layer of security (and privacy), as such, it includes most settings you will find on every Android phone, with additional security (and privacy) features.
Since you're coming from Samsung, you might be slightly disappointed in some aspects, because Samsung phones are at times very feature-heavy (my way of saying that it packs a ton of software settings compared to your average phone).
A way of seeing it, is that since Samsung has a very heavily modified version of Android, they are pretty far away from what's standard, and as such, what you will find on GrapheneOS will be much closer to other phones compared to your Samsung.
Now as for the technical aspects, I will let someone else answer.