You can file a lawsuit in federal court under which of the following circumstances?

Any time you want to sue someone regardless of the topic or residency of the parties

Only if the lawsuit is about a statute passed by Congress.

Anytime the plaintiff and defendant are from different states you can get into federal court $($regardless of how much money the Plaintiff is suing for as damages, since diversity jurisdiction is not about the money at all.

If the lawsuit is based on a federal statute or based on diversity of citizenship between the plaintiff and defendant plus the amount being sued on is over a certain dollar amount