I sold a property in Germany in 2020 and had to pay a capital gains property tax of 12k to the German tax authority; how can I reclaim the tax in the US?

You go through the foreign tax credit section of TT. See below for how to get to it. The regular interview will get you there but it is very easy to miss the relevant question.

However, you should be aware that the US foreign tax credit applies category by category and is further limited by the proportion of the categories US tax times the category's foreign income divided by the category's worldwide income.

Because US capital gains rates are so low (could even be zero depending upon your income) you may not have much, if any, US gains tax to offset. You don't get to apply the $12k of foreign capital gains tax against US tax from non-passive income (e.g. salary).

https://ttlc.intuit.com/turbotax-support/en-us/help-article/import-export-data-files/enter-foreign-tax-credit-form-1116-deduction/L5jnSn5Vm_US_en_US?uid=lrxwq9lh