Whenever sizes are suggested for social media, they’re often at the lowest resolution possible, so I always take them as a ratio.
If you’re using Canva for your graphics, they have different sizes of template for different social media platforms. But I’ve noticed they produce really low resolution results that can often look blurry, especially if you put photos on them.
To get them looking super high resolution and sharp you need to create the template at a larger size. For example, if the guide says create an Instagram post at 1080px x 1080px then I would double that to 2160px x 2160px.
As long as the file is smaller than around 3mb then it should be fine for social media, and mean that they look their best even on high resolution phones.