It is possible to get a legitimate Sole Proprietership going without much effort or paperwork. If you can think of a hobby that could be turned into a side-hustle, you could probably turn that into a functioning Sole Prop pretty easily. You can get some general info here: https://www.sba.gov/content/sole-proprietorship

If you go the Sole Prop route, you can start applying for Business credit cards right away. It is often done using your legal name (First Name Last Name) as the business name and your personal Social Security number to apply. As long as you have good personal credit, some of the major credit card issuers will likely approve you for business credit cards without requiring any real documentation for the business.

That said, a lot of people who want Business credit cards don’t go through any formalities and don’t actually operate their ‘Business’ for profit. Once you get approved for the credit card, the issuers don’t generally seem to care what happens to the business going forward.