Replace cv2.VideoCapture(camera_id) to cv2.VideoCapture("gst-launch-1.0 v4l2src device=/dev/video" + str(camera_id) + " io-mode=2 ! image/jpeg, width=1920, height=1080, framerate=30/1, format=MJPG ! jpegdec ! videoconvert ! appsink", cv2.CAP_GSTREAMER)

jpegdec can be replaced with hardware acceleration plugins, eg. On rk3588 it's mppjpegdec.