If you mark the Maximize box, TurboTax ignores whatever you put in the dollar-amount boxes when calculating your maximum permissible contribution. If 2020 TurboTax presently is indicating that your maximum deductible self-employment contribution is any amount less than $19,000, it means that you only have enough net earnings to support a total contribution of what TurboTax is telling you. Nothing about the behavior in 2020 TurboTax appears to have changed from 2019 TurboTax. Apparently the difference is because you have less profit in 2020 than in 2019.
