Not sure if this is a bug or something that needs improving but I found out that Bixby on my S21 Ultra randomly pops up (while the phone is in my pocket or bag) and speaks to me "sorry, I didn't quite get that". Bixby function is also turned off on my mobile because of this but still it happens and it really makes the experience of the S21 Ultra a lot less enjoyable.
@alx___9: To troubleshoot the issue, please head to Settings > Advanced features > Side key, and disable Open Bixby or Wake Bixby in the Double press and Press and hold categories. Furthermore, head to Settings > Display > Accidental touch protection, and toggle this option on. This will protect your S21 Ultra from accidental touches when it's in a dark place, such as your pocket or bag. Let me know if this helps.