If a LLC doesn’t file as a corporation on federal income tax, what are other options?

You may have the option of not filing federal taxes, from this IRS page.

A domestic partnership must file an information return, unless it neither receives gross income nor pays or incurs any amount treated as a deduction or credit for federal tax purposes.

If you wish to file, and it is a single-member LLC, you can file as a sole proprietor. Use schedule C in your personal taxes.

Partnership, C-corp and S-corp are the other options, discussed here.