Thanks Jason,
the Memory Leak is fixed  after saving the handPose model in a variable (_handPoseModel: HandPose) in HandGestureService and wrapping model.estimateHands(video).then(..) in video.addEventListener('loadeddata', (e) => {..})
The solution is available here: https://github.com/rakia/ng-dynamic-stepper/blob/master/projects/dynamic-stepper/src/lib/ml/hand-gesture.service.ts 3
and an article about it is available here 6.