I have found this question. However I think this has changed on API version 1.1.
If I use the search/tweets method, how can I see if the tweet is a RT?
search/tweets
To the ones who are using Hydrator1 and relying on its CSV export of the hydrated JSONL file: you can check reweet_id (no it's not a typo in version 0.0.12), and if it's NA then it's an original tweet as I found.
Hydrator
CSV
JSONL
reweet_id
0.0.12
NA
original_twitter_tweets = twitter_csv_data %>% filter(is.na(reweet_id))