TDLR; Solution by using online donation account.
None of the options worked for me. And my TurboTax 2020 desktop app had "Change my deduction" > "Itemized deductions... $[prefilled amount]" which took off 2k from my refund.. and didn't solve the problem. I tried going into the forms and manually changing numbers around. Nothing.
SOLUTION for me: After hours of frustration and anguish reading all these responses with no solution. I went and created an account online for their new donation portal ItsDeductibleOnline.com and meticulously re-entered every charity and every single thing I donated. Then, deleted all of the entries in my TurboTax charitable donations section, and imported entries from ItsDeductibleOnline account.
What it did: It changed my refund because it actually pushed some of my donations to next year overflow, which I guess the TurboTax app didn't do originally? So it didn't put the max 300 in the field for donation amount, but added forms with the overflowed donations for you to claim in 2021.
