If my soc sec payments in 3020 were$28063, minus the medicate deductions of $1735 then why wouldn’t the AGI on my 2020 form be $26328?

If Social Security is your only income, none of the Social Security is taxable, so your AGI is zero. On your 2020 Form 1040, line 6a is your total Social Security benefits, $28,063, and line 6b is the taxable amount, which is zero or blank.

 the gross amount of your SS benefits goes on your tax return line 6a.

You don't subtract any Medicare payments.