Sketchfab writes:
Every December, we challenge you to finish the year by testing your 3D skills with daily art prompts—and this year is no exception!
The art challenge is simple: create one model per day for 21 days using the prompts that we provide. Upload each of your models to Sketchfab and tag them #3December2021 and #Challenge.
Full participation details are available below. To give or get feedback on challenge entries, head over to the Sketchfab Forum or Discord. And to see all the entries, check out the tag gallery.