Yes, I'm sorry, I misunderstood your question. If you received $2,500 from your FSA in 2020, and only one spouse had income, then the entire amount on Box 10 of W2 will be included as income in 2020.
In Turbo Tax, you are asked to enter any amounts from your FSA that were not distributed to you for qualified expenses. Any remaining amount in your account will be have to be entered on that screen and will be forfeited in 2020. The forfeited amount would reduce the taxable amount in Box 10 of W2. FSA doesn't allow rollover on any remaining amount from the plan.
This is from the link on the screen "I want to know more about this" on the screen "Any leftover from your Flexible Spending Account ?".
Any money that was not reimbursed because you did not incur enough qualified dependent expense count as being forfeited:
For example, under your employer plan, you have $5,000 pretax amount towards dependent care, and you only incurred $4,500 so the remaining $50 would be forfeited. You would either enter $50, in this screen, the amount forfeited, or $50 carryover into next year, if permitted by your employer.
