According to IRS Publication 526, there are three contributions that may qualify for the 100% limit.
Qualified Cash Contributions
Generally, the amount an individual can deduct for charitable cash contributions is limited to a percentage of the taxpayer's adjusted gross income. After tax year 2021, qualified contributions are not limited based on a percentage of adjusted gross income. However, they may be limited if they exceed the amount on Form 1040 line 11. Refer to Publication 526 for details
Qualified Conservation contributions of farmers and ranchers
You are a qualified farmer or rancher if more than 50% of your gross income for the year is from farming. The deduction for qualified ranchers or farmers making a qualified conservation contribution is limited to 100% of their AGI minus any deductions for all other charitable contributions. "However, if the donated property is used in agriculture or livestock production (or is available for such production), the contribution must be subject to a restriction that the property remain available for such production. If not, the limit is 50%."