YouTube will automatically compress all videos. Engineers can update the compression algorithm as long as they think fit. Although the compression algorithm they use works well in most situations, it may not always work for your videos.
So if you send a 4K high quality video (3840×2160) YouTube will compress the video with all possible resolutions: 4K (3840×2160), 2K (2560x1440p), full HD (1920×1080), 720p (1280×720) and standard resolution versions 576p, 480p….
Step 1: Open your YouTube app, tap on your profile picture on the top rightand corner.
Step 2: From the left menu, select Settings and tap on it.
Step 3: Find Upload quality and tap on that. Once Upload quality opens, you will see a range from 360p to Full Quality. Full quality can make sure your videos are smooth and clear. You can choose what you want but i would chose the "Full Quality"
Step 4: Select Save.
If you encode your video as 480p, YouTube will not and cannot expand it to 720p or 1080p. If you want to make the video look good on YouTube, you need to provide the highest possible resolution. The same is true for bitrate. High bitrate video looks smoother than low bitrate video.