If you want to dive into tax-speak, IRS Notice 2025-69 allows individuals who receive a 1099 to use contemporaneous records to substantiate their tip income for 2025 if it isn't specifically set out on the 1099. (You'll find the fun part around page 16.)
They have not addressed what to do if you earn less than the threshold for receiving a 1099. TurboTax does have a place to report this when you enter your income for Schedule C. If say you work for Uber, but only made $400, go ahead and report it as cash income. There's a check box for "tips". On the next screen you want to say this "should" have been reported on a 1099, and enter the tip amount.
Right now there's no IRS guidance that would allow you to claim the tip. However, TurboTax has a statement that they will reach out if the IRS provides further guidance that would allow you to claim the deduction.
