I don't know if it's just me or if anyone else experiences it but the Video in S21 Ultras camera feels really jittery and it has this weird thing where when you move your S21 while taking q video, it's kinda like the video shifts to the other side as if it is warping to the other side of where you want your video to focus on. Also personally for me I don't know if it's the lenses themselves or because the lense are too big but I feel like instead of Samsung adding more cameras every year, they should improve their camera software quality specially the Camera Lag and the Video. Let's be honest, the images look amazing and the zoom looks fantastic but the video software in the camera is really bad and I hope that you can fix these issues. If not the S21 line up then I hope you fix the issue for the upcoming S22 ultra or Note 22 ultra because I really love Samsung and I really want damsung to improve in all of the aspects. It personally pains me to see youtubers making fun of Samsung specially the video quality and I hope that they could fix this. Also I hope that Samsung would cooperate with app companies to optimize the Camera software such as Snapchat, Instagram, Facebook, Twitter etc. Because it also really lacks im these areas.
Turn off video stabilization in the settings menu that stops the auto rotating when the phone stops moving during a video. Is your video jittery when you play it back? Is it cutting off parts of the frame or just feels shaky, and is you phone on the most recent update?