If you've read Publication 526, you are aware that charitable organizations qualified to receive contributions that an individual taxpayer may deduct are in two categories. The first category is 50% limit organizations, which includes your publicly-supported charities, churches, and educational organizations, and the second category is the rest of them.
Generally, contributions to 50% limit organizations are limited to 60% of AGI. That's confusing, but I don't write the tax code. But there are circumstances in which a qualified cash contribution is limited to 100% of AGI if the taxpayer elects to apply the 100% limit.
Because of the weirdness in 2020 in which retired taxpayers weren't required to take required minimum distribution from IRAs, the 2020 transcript notes that IRS knocked the charitable contribution down to
60%. I vaguely recall reading this in the Publication 526 when I was preparing this tax return.Reading the instructions for Schedule A Line 11, I was supposed to note the treat as qualified contributions election for a 100% on the dotted line to the left of the entry for Line 11.
I missed that. Aargh.