Many factors at work here.

First off, mp3 at 320 kbps (or 256 for that matter) encoded with modern algorithms will be nearly idrntical to the original source. I defy you to reliably tell it apart from a FLAC in an A/B test. Where it usually fails is in stereo imaging, not obvious distortion or frequency limitations.

Secondly, many people have mentioned normalization (actually compression) in streaming services. When applied after the mix, i.e. exactly what they do, it ruins music. If you can turn off every ‘feature’ in these services that modifies the sound, you’ll find improvements.

Thirdly, you’re not necessarily getting great sound from them anyway. Spotify defaults to 96kbps Vorbis which is comparable to 128kbps mp3. And if your network speeds are low or laggy, it may well drop the quality dynamically to keep playing without glitches.

Fourth, there’s the issue of mastering. You may have a differently-mastered release than what is on the streaming site. This can make a HUGE difference in some cases. If you can, try listening to Dark Side of the Moon releases from 2003 (Doug Sax) vs. the 2023 blu-ray.

And those are only the most likely candidates. There could well be other factors at play.