The ideal vertical video dimension is made in portrait with a 9:16 aspect ratio and the ideal dimensions being 1080×1920 pixels. Understanding the ideal dimension for vertical videos is crucial to capturing your audience's attention in this ever-evolving social media landscape.
https://clipchamp.com/en/blog/best-practices-creating-vertical-videos-smartphone/
16:9 resolutions
The screen size of computer monitors or TV sets gives you an idea of the aspect ratio through its physical dimensions, but it’s not an indication of the screen resolution, because even a large screen can have a low resolution. For a 16:9 resolution, the width is divisible by 16 and the height is divisible by 9.
The screen resolution tells you the number of individual pixels in one horizontal line and the number of these lines, making up the width and height. The total amount of pixels results from multiplying one value by the other. The aspect ratio is the relationship between width and height, as the resolution numbers will be multiples of 16 and 9 for the widescreen format. We’ll give you an overview of common resolutions
https://boords.com/blog/what-is-16-9-aspect-ratio-definition-and-examples