How do I report interest earned from repayment of a personal loan I made to a family member. ?

You're correct, you only need to report the interest.  You'll simply go through the same path as if you were entering your information with a Form 1099-INT, entering any information you have.

 

To enter interest without a Form 1099-INT in TurboTax Online:

1. If you don’t see 2022 TAXES in the left pane, select the dropdown to the right of Income & Expenses on the Hi, let’s keep working on your taxes! page and then select Let’s get started, Pick up where you left off, or Review/Edit. 
   • Otherwise, in the left pane, select Federal, then Wages & Income (This is labelled Income & Expenses in TurboTax Self-Employed)
2. Scroll down and select the Show more dropdown to the right of Investments & Savings 
3. Select  Start or Revisit to the right of Interest on 1099-INT
4. Select  Yes on the Did you receive any investment income? screen, then select Continue
   • If you see either the Your investments & savings or Here's your 1099-INT info screen, select Add investments or Add another 1099-INT as appropriate, then select Continue
5. On the  Let's import your tax info screen, select Enter a different way
6. On the  OK, let's start with one investment type screen, select Interest, then Continue
7. On the  How would you like to upload your 1099-INT? screen, select Type it in myself
8. Type in all available information

Please see the TurboTax Help article What if I didn't get a 1099-INT from my bank? for an alternate entry procedure.

In case of the desktop version, would that be under "Interest and Dividends" section for "Personal Income"?

Using TurboTax Desktop, click Personal

Personal Income

Interest and Dividends

Interest on 1099-INT   START

Select "Type it in myself"

Enter the family member's name and the amount. 

 

You can select "NO" to providing their Federal ID Number