Larger in terms of estimated population size when the city was thriving.

Read "larger than any city found there thus far" as "larger than any precolonial city found inside of the current Amazon rainforest as of 2024-09-15".

This question is intended to close on 2025-12-31. If larger cities are found after that, but not before the question still resolves NO.

https://www.bbc.com/news/science-environment-67940671

https://www.theguardian.com/science/2024/jan/11/amazon-archaeology-lost-cities-ecuador

https://nebula.tv/videos/reallifelore-whats-hidden-under-the-amazon-rainforest/

I'm no archeologist and will defer to expert opinion if there is contention, plausibly resolving this to a prob or to N/A.