Hi! Is there a difference in pronunciation between pije and piję? I can't seem to hear a difference.
Text to speech used on doulingo pronounces them exactly the same. all final "ę" like Polish "e"
In real life it is complicated. Some people pronounce them exactly the same, some pronounce "piję" with a slight nasality. Even the language books (for Poles) disagree, some say you should pronounce final ę as "e" but may add nasality when it's ambiguous like with "piję", others say you it's better to always use slight nasality, especially when it's ambiguous, but not using that is acceptable in "common speech".
Both agree you should not "overdo" the nasality.
Most of Poles don't pronounce ę at the end of words, we rather tend to pronounce it as e. In fact, if someone does it, it might seem a bit pretentious or protectional. We even have this funny term "Ą Ę " or "bułkĘ przez bibułkĘ" (with strongly pronounced ę) for people who act very protectional towards the others.