Hi Ayala Or-el,
Welcome to Microsoft Q&A forum. I'm happy to help.
It seems your computer were playing surround sound codec from streaming platform while your system is currently configured as stereo output.
Some movies support both surround sound and stereo as separate audio tracks, please do troubleshoot by changing audio track to a stereo one to see if you get louder sound.
If you have any updates, please feel free to let me know.
Thank you for your time.