I dumped the contents of the 19.07 and 21.02 ipks.
19.07/etc/init.d/mjpg-streamer
19.07/etc/hotplug.d/usb/20-mjpg-streamer
19.07/etc/config/mjpg-streamer
19.07/control.tar.gz
19.07/data.tar.gz
19.07/usr/lib/output_http.so
19.07/usr/lib/input_uvc.so
19.07/usr/bin/mjpg_streamer
19.07/www/webcam/index.html
19.07/debian-binary
21.02/etc/init.d/mjpg-streamer
21.02/etc/hotplug.d/usb/20-mjpg-streamer
21.02/etc/config/mjpg-streamer
21.02/control.tar.gz
21.02/data.tar.gz
21.02/usr/bin/mjpg_streamer
21.02/debian-binary
mjpg-streamer 19.07 installs some plugins and extra files, output_http.so, input_uvc.so and /www/webcam/index.html. In 21.02 they're moved into their own packages.
mjpg-streamer-input-file
mjpg-streamer-input-http
mjpg-streamer-input-uvc
mjpg-streamer-output-file
mjpg-streamer-output-http
mjpg-streamer-output-rtsp
mjpg-streamer-output-zmq
mjpg-streamer-www
mjpg-streamer-www-simple