Humaaans: Mix-&-Match illustration library
Customizable 2D illustrations of people. These images are licensed CC0, so they're free to use.
Free to Use Clip Art Images & Vector Illustrations | ManyPixels
Free illustrations. This isn't a huge library, but you can download them as SVGs and customize the images. There are some images of people that could potentially be used for characters in a scenario with some customization.
unDraw - Open source illustrations for any idea
Image library that you can easily customize. These characters might work in some scenarios, but they don't have facial expressions. Available in SVG and PNG.
App
Artflow has tools for creating character images and videos with automated voices. The free version is for noncommercial use only, but the paid plans can be used for commercial uses. The samples have some AI weirdness as is seen in a lot of the image to video conversions, but this looks like a fun tool to explore.
25 Free Illustrated Characters - Downloads - E-Learning Heroes
Tom Kuhlmann created illustrated characters in different poses using Midjourney and then cleaned them up afterwards. He's sharing these results for free. Note that some images may still have some weird artifacts, even after the cleanup. These would be a great resource for people looking for a free character set for a portfolio sample.
Reface – AI Face Swap App & Video Face Swaps
A collection of AI image and video tools. I saw an example of a comic created by face swapping AI-generated images with a photo of a real person. This kind of technology might be a way to generate multiple images of a character in different poses and with varied expressions but with consistency in features.