Hi, please see the following FAQ: https://ttlc.intuit.com/questions/2963870-how-do-i-enter-a-large-number-of-stock-transactions-in-tur...
TurboTax Online is equipped to handle around 500 individual transactions (give or take) per brokerage account before the performance starts to deteriorate.
If you need to enter a bunch of stock transactions with a total sales volume of less than $10,000,000 (ten million), you can enter a summary for each sales category.
Another alternative is to switch to the TurboTax CD/Download software which handles around 2,000 individual transactions per brokerage.