If you started receiving VA disability benefits when you retired in 2020, then your military pension payment were taxable starting in 2020 and all future tax years.
In Publication 525 there is a good example of when you can claim the pensions received for prior tax years as not taxable - https://www.irs.gov/pub/irs-pdf/p525.pdf#page=19
Example 19. You retired in 2017 and receive a pension based on your years of service. On August 3, 2023, you receive a determination of service-connected disability retroactive to 2017. Generally, you could claim a refund for the taxes paid on your pension for 2020, 2021, and 2022. However, under the special limitation
period, you can also file a claim for 2019 as long as you file the claim by August 3, 2024. You can't file a claim for 2017 and 2018 because those tax years began more than 5 years before the determination.
Since you have been receiving VA disability benefits for the past three + tax years, 2020 thru 2023, your pension payments are taxable since they do not include any disability payments. The pension is only based upon your years of service.
Also, I am a Viet Nam veteran but not a retiree.
