Tax Year Prior to 2020: I paid $12,000 for an unpaid internship in 2019. Can I deduct this or take an education tax credit? I graduated in 2018.

It doesn't look like you qualify for the American Opportunity Tax Credit (AOTC) but can take the Lifetime Learning Credit (LLC). If you receive a tuition statement, then you have a case and may be able to take the LLC. However, the LLC is not a refundable credit. So, you can use the credit to pay any tax you owe but you won't receive any of the credit back as a refund.

Probably (almost certainly) not, but what are the details.  Since you graduated in 2018; it appears that this internship was not part of the school program. Who did you pay and why? You must have paid an "eligible institution" as well as paid "qualifying educational expenses ("tuition").