Here are the correct instructions, confirmed with a live tax-expert on TurboTax. Please ignore the other sets of instructions. They may have the same end-result, but they will complicate things.

(for mobile browser version of TurboTax, probably also app version)

1. Automatically import your 1099-MISC via the Robinhood integration option (search for Robinhood if you need to). Should be similar for Acorns, E-trade, etc.
2. Click ‘take me to my return’.
3. Click ‘Federal’
4. Click ‘Wages & Income’ tab (may already be selected)
5. On the second line under your W2 you should see: 
   Income from Form 1099-MISC
   Robinhood Securities LLC
6. Click ‘Edit’ for that.
7. Click the First radio button for ‘xx-xxxxxxx‘.
8. Make sure box 3 shows the extra income amount.
9. Type in ‘investing’ or whatever you want for the name 
10. Click ‘none of these apply’ for uncommon situations
11. Click ‘no it didn’t involve work like my day job’
12. Click ‘I got it in 2019’
13. Click ‘No it didn’t involve intent to make money.’ (TT does a horrible job of phrasing this, and the help text doesn’t help. Despite the fact that we CLEARLY intended to make money and knew there would be dividends, apparently this is not a real job and doesn’t involve intent in the same way. TT really needs to fix this.)
14. Click ‘No’ for another 1099-MISC form.

You should see it in Your Income list with no errors or warnings. When you proceed with the submission it should no longer mark this as undeclared income or self-employment tax.

Declaring stock dividends should be WAY simpler than this.

Since you did receive a 1099-MISC, the above instructions are the right way to enter the 1099-MISC as other income and not self-employment.  Most dividends are reported on a 1099-DIV so this is a rare situation.  It is entered in the 1099-MISC section, but you must indicate that it was derived from activities without a profit motive.  If you answer Yes, to the intent to earn money question, the income will transfer to self-employment.   If you enter it in the miscellaneous income section and answer No, to the intent to make money question, it will be reported the exact same way, but you won't be including the issuer's name and Federal ID number with your tax return.  

Self-employment is usually reported in Box 7 (the IRS expects a Schedule C), whereas ''Other Income'' is reported in Box 3, and no Schedule C is required.    @Labutin @jasonsbacon