ALL of your combined income must be entered on your joint tax return. If you both have a SSA1099, then you enter both of them. The income entry screen will ask which one of you the SSA1099 is for and give you a spot with your name on it.
Go to Federal> Wages & Income>>Retirement Plans and Social Security (SSA1099 and 1099RRB) to enter your SSA1099.
LUMP SUM PAYMENT FOR FAIRNESS ACT
Your 2025 SSA1099 will show the extra payment you received in 2025 as a result of the Fairness Act. Look in the bottom left corner. It will say something like “Includes $XXXX Paid in 2025 for 2024.
When the software asks if you have a lump sum payment say yes. The program will help to determine if is better for you to attribute the sum to 2024 or to 2025, based on your AGI for each of those years. This will all be done within the 2025 program; you do not amend 2024.
https://www.irs.gov/faqs/social-security-income/back-payments/back-payments