I play Minecraft on my Laptop.

The Bug has to do when you launch Minecraft Java from the Minecraft Launcher. When I start the game with no headphones plugged in the Game continues to play over the speakers even though I plugged in the headphones later. To get the sound over the headphones is only possible when headphones are plugged in before I start Minecraft from the Launcher.

The Version of Minecraft does not matter, this bug exists since 1.7.10 and 1.12.2, because I played heavily modded version on those version and thought it has to do with those many mods and forge. Now I started to play Vanilla (clean) 1.16.3 and the same bug still exists.

Also, I change PC/Laptop three times in between this bug exists.