EDIT: The only reason why I still had it at this point was because I could use it with other apps. However, now that my Spotify Subscription is cancelled, it doesn't work with anything. It's mildly infuriating because today, I can't still use it with other apps like I was able to yesterday.
Please don't make the same mistake I made. No one should buy this.
When playing music from USB-C the audio precessing is happening in the adapter, not the phone. You may want to get a different/better adapter and that should solve your problem with low volume.
This one from Amazon sounds good, gets crazy loud, and is very inexpensive:
USB Type C to 3.5mm Female Headphone Jack Adapter https://a.co/d/40sa5qF