The idea that rape can only be committed with a penis is an artifact of English common law. Most countries even in the Anglophone world that the British once colonized no longer define rape in this way. In the UK, rape still requires penetration by a penis. But this is not how rape is defined most other countries.

The link I provided above says:

In 2011, Adree Edmo raped a 15-year-old, performing oral sex on the underage boy after the teen fell asleep on the couch at a house party. Mr Edmo pleaded guilty to the crime of sexual abuse of a minor under 16.

https://www.womenarehuman.com/transgender-child-rapist-lauded-as-civil-rights-hero/

In the US, there is no one definition of rape that holds true across all states and territories. But the FBI's Uniform Crime Reporting system defines rape as

Penetration, no matter how slight, of the vagina or anus with any body part or object, or oral penetration by a sex organ of another person, without the consent of the victim.

https://ucr.fbi.gov/crime-in-the-u.s/2013/crime-in-the-u.s.-2013/violent-crime/rape#:~:text=The%20revised%20UCR%20definition%20of,the%20consent%20of%20the%20victim.

I thought American statutes were strict rape/sexual assult can only be committed using a penis (therefore, only males can commit rape).

Sexual assault and rape are not the same thing! At all. Sexual assault can be committed by people of either sex, and does not require penetration.