Clarification regarding bonus clawback and 401(k)

I received a sign on bonus of 70k USD back in 2024, which was subject to a full clawback if I left within two years. A significant part of that bonus was secreted into a 401(k) account. Now that I am leaving the company without completing two years, I need to return the entire bonus (less FICA as per the agreement). My question is how this should be correctly handled for tax purposes.

I understand that I can do an itemized deduction of the repayment amount when I file 2026 taxes. Another option I have is IRC 1341 tax credit which I will receive for the overpayment of 2024 tax for the bonus that I am now repaying. I understand that for the second, I should not include the 15k in 401(k) because I did not pay taxes on it. For the first (deduction), can I include the entire repayment amount, or do I again need to exclude the 401(k) amount because it was not in Box 1 of my 2024 W-2?

I am thinking about a Roth conversion this year, and so expect to pay taxes on the withdrawal amount. But, since I am having to pay it back, it would mean I am paying income tax on money that I did not receive.