Turbotax says my Maximum FHSA deduction available for 2023: $0.00. I've never contributed before 2023 to a FHSA so it should be 8000$. How do I fix this??

You need to enter your contributions before your deduction limit can be calculated. To do so you’ll need to enter the information from your T4FHSA - First Home Savings Account Statement. Once you enter the slip, TurboTax will adjust your deduction limit.