Talking in an xbox party or discord call while running vibrant visuals causes extreme fps drops. Otherwise running a normal or modded survial world with maxed settings can easily reach 60+ fps when not in a party or call, or doing an action that transmits audio to other users. I believe this is an allocation issue on minecraft side, or the xbox hardware.
I am uploading this bug for someone else, could others please confirm/verify this affects them too.
This issue is being tracked at MCPE-199201.