Difficult question because Appian increase this number in some updates. Today, they have it as follows:

1. Standard Tier: Supports up to 4 million rows per record type.
2. Advanced Tier: Supports up to 20 million rows per record type.
3. Premium Tier: Has no set row limit for synced record types

It's very worth it to check this before an interview. Your reply should be for the last Appian version as you should be up-to-date.

https://docs.appian.com/suite/help/26.7/about-data-sync.html