The correct tax treatment of the reimbursement that Leon received in 2023 for a medical expense that he deducted on his 2022 Schedule A is:
The recovery is includable in income in the year received up to the amount by which the deduction or credit claimed reduced taxes in the prior year.
This is consistent with the tax principle known as the "tax benefit rule." If Leon deducted an amount in 2022 and received a reimbursement in 2023, he needs to include that amount as income to the extent it provided a tax benefit in the prior year. He does not need to amend the prior year's return, nor should he deduct the recovered amount again on his 2023 return.