LucidChart has an embarrassingly low count and quality of user icons. I would argue that a User icon is one of the most commonly used icons aside from basic shapes.
Here is LucidChart’s result for User in the shapes library:

The top result isn’t even “User icon” and leads to a blank image. The rest of the images are either irrelevant, have extra adornments, or are of low quality. For contrast, here is a set of user icons found on Google image search:
