I was preparing a similar post! So there are very important changes in the camera software with the bullseye release. With this release is installed a new stack based on libcamera and applications equivalent to raspistill, raspivid,… The old applications based on MMAL including the Python Picamera library are no longer available (but it would be possible to reactivate them?). A new officially supported python library would be under development. So for Picamera users it is absolutely necessary to stay with Buster until all this stabilizes.
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