In general, for USA Softball bats must bear the USA Softball certification mark, be on the approved list, and not be on the "non-approved" list.
Based on your question, I'm guessing you saw the exception in the 2023 rulebook in Rule 3.1:
Exception: Any bats bearing the USA Softball, USSSA, or WBSC Certification marks and pass our Fast Pitch Compression testing thresholds are allowed in the USA Softball Men’s Major and Men’s Open Fast Pitch Championships.