How can I add Form 8949 with Turbo Tax so don't have to mail it in

The Form 8949 Sales and Other Dispositions of Capital Assets is completed by the TurboTax program when you enter an investment sale.

To enter an investment sale -

Click on Federal Taxes (Personal using Home and Business)
Click on Wages and Income (Personal Income using Home and Business)
Click on I'll choose what I work on (if shown)
Under Investment Income
On Stocks, Cryptocurrency, Mutual Funds, Bonds, Other, click the start or update button

Or enter investment sales in the Search box located in the upper right of the program screen. Click on Jump to investment sales

Using the online editions -

On the screen Did you have investment income in 2024? click on Yes

On the screen Let's import your tax info click on Enter a different way

On the screen OK, let's start with one investment type, select the Investment Type and Continue

On the screen Tell us more about this sale enter a Name and Continue

On the following screen select the type of investment sale on the dropdown What type of investment did you sell?

if you're referring to the ask to mail stuff in after inputting 1099-B at summary level but it has adjustments for wash sales or AMD etc; then inputting specific sales from 1099-B as "one by one" instead of sales summaries should generate 8949 for those entries and remove the need to mail things in.  you can enter as a mix, just put the lots/sales with adjustments as one-by-one; and calculate the balance remaining of the 1099-B to input as a summary.

(experience based on desktop version but presumably online is similar)