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.
Steplab Character Set and Custom Illustrations — Marinastu
This illustrator created a set of characters for schools. Might be worth pricing out if custom illustrations are needed.
40+ DIY Vector Kits to Create Your Own Character in Adobe Illustrator
A collection of vector illustrations for character sets. These are various sets from different sources and in different styles, but all of these include some mix-and-match vector elements like clothes, props, and sometimes facial expressions and poses.
StoryTribe: Effortless Storyboarding for Everyone
This tool isn't designed for elearning storyboarding, but it has customizable illustrated characters plus props and backgrounds that make it an possible choice for branching scenarios.
Beginner's Guide to Midjourney Consistent Characters.
Tips from Rory Flynn on how to use Midjourney to create consistent characters. This shows how to use CREF in your prompts, with sample prompts and a few tips to improve your results