Is the default for a foreign single owner LLC a disregarded entity? Or do I need to file Form 8828 to make that designation?

A US LLC is by default a disregarded entity. Absent an election, it is treated as either a sole proprietorship for a single member or a partnership for more than 1 member.

The answer is a bit more complicated when the company is a foreign LLC. A foreign LLC needs to file Form 8832 in order to be treated as a disregarded entity if it has more than 1 member; otherwise, it is treated as a foreign corporation. The election must also be made within 75 days of the tax year.