Why does sound quality change when I open games in full screen?

Hi, I recently bought a new Macbook Air 2020. I usually use it with a set of bluetooth earbuds (not airpods). Whenever I open a game in full screen, (mostly League of Legends, but also other games) the sound becomes much darker. This is especially apparent when I listen to podcasts or talk with people in voice chat. Their voices become almost unrecognisable. Why is this happening and is there a way to fix it? Occured both in the original OS and in Sonoma.