For example, this baseball icon:
https://svgmix.com/item/yBq8JY/ball-baseball
says that it is licensed under the "MIT License". That means that, if you embed the icon in a product, you're obligated to document the fact that the icon is copyrighted by its author and explain what license you used it under.
The link they offer for the license is this one: https://opensource.org/license/mit/
It just says "Copyright "... they don't offer you any way to identify the actual copyright holder and credit them according to the license they claim for the icon.
That's bad. To the point of making it nearly impossible to reuse these freely offered icons.