How do I know if the American opportunity credit has been maxed out as a dependent on parents previous tax forms? Halftime Junior

You have to ask your parents.  If they don't remember, they can look at their past returns.  If they don't have copies,  free transcripts from the IRS will show the education credit.  There is a fee for getting copies of actual tax returns from the IRS.

See https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-get-a-copy-of-a-return-i-filed-this-year-in-turbotax-online/00/25932

https://www.irs.gov/individuals/get-transcript

The only way to find out is to ask your parents to check Form 8863 on their returns for the years you were claimed as a dependent while in college.

Even If you no longer qualify for the American Opportunity Credit, you might qualify for the Lifetime Learning Credit

There's no limit on the number of years you can use this credit for undergraduate, graduate and professional degree courses, including ones to improve job skills.

• Maximum credit is $2,000 per tax return.
• Can be used when you're only taking one class.
• You don't need to be working toward a degree.
• None of the credit is refundable.

To qualify for the credit:

1. You, your dependent, or a third party paid qualified education expenses for higher education
2. The qualified education expenses were for an eligible student
3. The eligible student is you, your spouse, or a dependent on your tax return.
4.  For the full credit, your 2021 MAGI (modified adjusted gross income) is less than $59,000 ($119,000 if you are filing jointly)
5. For a reduced credit, your MAGI is between $59,000 and $69,000 ($119,000 and $139,000 if you're filing jointly)