Where can I find free models to practice with cam software?

I'm learning 5-axis machining on the job, which is useful, but I want to get a better intuitive sense of the multi axis toolpaths

So I was wanting something to practice on that can't be done with just 3+2 axis toolpaths, but also fun, like a bust or skull, something interesting that I could make if I had the time over the weekend

Ideally it would be a fusion file, but a step file would work as well

Would an STL file work or are those too low resolution for what I'm wanting to do?