Hey sea of green. Although ETS only has a few official essay questions in test format, it does provide a pool of essay topics. For example, the Issue pool is provided from ETS at this link:
Introduction to the GRE Issue Task (For Test Takers)
Overall, I'd recommend practicing with questions that are directly from ETS or are adapted specifically to resemble the structure and difficulty level of ETS questions. Way too many GRE questions are floating out there where clearly the goal is to just write really hard questions, get you to struggle and bang your head against the wall, but then claim that pain that you feel is "improvement" lol. So yeah, definitely focus on the ETS questions first, making sure you understand how to do as many of them as possible.