A private investment is completely worthless as the company was dissolved at the end of the year. Can I report this loss? How?

Yes, you can enter as Worthless stock.   To enter worthless stock as investment sales:

Under Federal Wages& Income, select Stocks, Cryptocurrency, Mutual Funds, Bonds, Other (1099-B) under Investments and Savings.

1. Did you have investment income in 2024? YES
2. Let's import your tax info  Enter a different way
3. OK, let's start with one investment type Other Continue
4. Tell us more about this sale  Worthless Stock Continue
5. Now, enter one sale for WORTHLESS STOCK (Proceeds=0 Date sold or disposed= 12/31/2024)
6. Let us know if any of these situations apply to this sale  This was a worthless security  Continue