Of course you can put it anywhere you’d like. Services like arXiv specialize in hosting pre-prints of published papers as well as white papers that only have an institutional association.

The problem is that the job of an academic is to publish. That’s how you build credibility and seniority. For it to count as a “published paper” it needs to have undergone peer review so that the people who want to read/cite the paper at least have the confidence that it’s at least been reviewed by other experts in the field.

There are some “journals” that will publish anything as long as they get their fees. Most academics are wise to that by now, but it can still impress people in business for whom a pub is a pub.