I no longer have a HDHP but have an HSA with funds. I do not contribute to the HSA. TurboTax asked if I was an "eligible individual" in Dec 2023 - why? Implications?

TurboTax is trying to find out if you used the last-month rule in 2023. The last-month rule states that if you are covered by an HDHP policy on December 1st, then you can use the full annual HSA contribution limit, no matter how few months you were covered.

The catch is that if you use the last month rule, then you must stay covered for the entire next year.

However, if you didn't use the last-month rule, then you are not penalized in the following year.

TurboTax always applies the last-month rule without telling you, so that you have no way of knowing if this applies to you or not.

Since you had an HDHP in 2023 and don't in 2024, this question does apply to people just like you. But if your HSA contributions in 2023 were less than what your annual HSA contribution limit would have been without the last-month rule, then you have nothing to worry about. But if you took advantage of the last-month rule to contribute more than you have otherwise, then you will have pay some additional tax.