&backgroundblur is a shortcut for &effects=3. It enables the ML-based background blur effect on the sender's video.
You can optionally pass a value to set the blur intensity (0-20). For example, &backgroundblur=5 applies a heavier blur. If no value is given, the default blur amount of 2 is used.
If the user manually adjusts the blur amount via the slider during a session, that value is remembered per room and streamID in localStorage and will be restored on the next visit.
