How do I report only one of my earnings as self employment?

TurboTax Self-Employed also allows entries for other earned and unearned income in the same sections as the form numbers.  So, you will enter your self-employment income  in that section and your W-2 income (if you received any) in that section.

Yes all your income and expenses go on the same tax return.  You can enter 1099NEC or cash Self Employment Income into Online Deluxe or Premier but if you have any expenses you will have to upgrade to the Self Employed version.

Where to enter expenses in the Online Self Employed version

https://ttlc.intuit.com/questions/3636848-where-do-i-enter-my-self-employment-business-expenses-like-home-office-vehicle-mileage-and-supplies