This bluetooth thread on Head-Fi is a good place to start,
though they don't seem to have much recent discussion of USB-C dongles.
The Verge reviews one pretty well, hopefully others here can chime in...
My experience has been that wired > wireless across all things digital,
and in audio the biggest factor is the drivers - where the sound is generated,
and a dongle will give you the greatest flexibility in auditioning IEMs & headphones.
Are you rooted? Viper4Android and other EQs make a big difference without adding hardware complexity.
This is the best option if you are rooted. It has great sound effects and works globally for all apps.
https://labs.xda-developers.com/store/app/com.pittvandewitt.viperfx
It also supports convolution equalizers like these. They equalize your headphones to sound as neutral as possible, in a way which isn't possible with a typical graphic equalizer.
Just stick with one.
Since you're posting in r/androidroot I'm going to assume you are rooted, and I recommend using Viper4Android as it's more than just an EQ.
How do you feel about rooting? I own over a dozen pairs of headphones/IEMs/earspaeakers/whatnot, and my daily drivers are a Pixel 3a and Jabra Elite 65t truly wireless.
I'm rooted and have Viper4Android sound mod running, so I can get exactly I want in my earholes.
I love mine, but if you're going to use head/earphones, I think Viper4Android is mandatory to tweak the sound,
which also means rooting.
The process is not nearly as tricky as in the past, and Magisk is a big part of that.
After quite a bit of fiddling (goes with the territory), I found a Viper4Android that works on my rooted 3a:
ViPER4Android FX 2.7.1.0 by Team DeWitt which installs from an .apk.
It doesn't seem to have profile saving/loading, but positive feedback should help that.
The main thing I use is the Surround mode(s) to open up the stage for IEMs
I mean this one https://labs.xda-developers.com/store/app/com.pittvandewitt.viperfx
You'll need to root your phone to use it. This one is the reason why i cannot live without root. After you've installed, play with the settings and you can feel the differences.
Damn. See if you can get AI to work with a point-click on some other switches, such as in Settings. If it works, then it's just AudioFX.
Aside: VIPER4Android is way better.