In the US at least this isn't really true, at least not in a practical way for most people.

Charitable donations are tax deductible true, but they are for most people covered under what is called the standard deduction, which is a standardized amount that aims to estimate would a regular person would be able to deduct from their taxes. The standard deduction is applied automatically and is $14,600. This means that if you don't do anything abnormal on you it taxes, your taxable income is reduced by the standard amount. For most people they wouldn't typically be able to find $14,600 in tax deductible expenses, so the standard is worth it.

The catch is that if you take the standard you cannot itemize, as taking the standard deduction is basically saying to the IRS "yea I donated here and there, bought some stuff for work, did this and that". Itemizing is listing out your individual tax deductible expenses (and justifying why they are deductible) so if for example you had a single year where you donated $20,000 you could itemize that instead of taking the standard deduction for a total reduction in income of 20k plus whatever you could come up with.

The other reason why that isn't really applicable is that a deduction is not a credit, that is to say, deductions reduce your total taxable income amount. If you deduct $1,000 (a 1k donation for example) that would have been taxed at 20% you will receive back from the IRS, $200. Meaning that you still had to pay $800 out of pocket for the donation that will not be refunded to you.

Deductions pretty much never result in getting more than the tax that you would have paid refunded. Even if youanahe to deduct more than you make, the resulting negative would just result in a carry over loss for the next year. You can effectively pay an income tax of 0 but it requires losses and other deductible expenses that are greater than your income, which means you didn't actually make any net income for the year (on paper and practically)

Other countries are different of course, but I wouldn't want someone going out and donating their life savings thinking they will get it back in tax season.