Do I have to enter money deposited in my HSA by a previous employer, if I didn't work in 2024 & didn't get a W-2?

You can enter the employer's contributions even if you didn't receive a W-2  with Code W in box 12.  Follow the instructions below for TurboTax Online:

1.  
2. Open TurboTax
3. Select Federal and Deductions & Credits
4. Scroll down to Medical and select HSA, MSA contributions
5. Go through the interview screens and select yes on the screen Did you put money into an HSA in 2024?
6. On the screen Did your employer tell you about any other contributions?, select Yes
7. Enter the amount in the box  Employer and payroll contributions not reported in Box 12 of your W-2.

Refer to the TurboTax article What Is the IRS Form 8889? for additional information.