I know that there is form DA-1 that people use to claim back on dividends taxed the the source. I am in a slightly different situation just for tax year 2023.
I moved back to Switzerland in 2023 and renounced my greencard, hence I am still have to pay taxes for whole 2023 in the US. I have earned interest and dividends on my IBKR account. As I am considered a US person for tax purposes I was not taxed at source. I have to pay income taxes in the US for 2023 on the interest and dividends. However, I also have to declare them on my Swiss tax form.
What I did now, I am claiming the interest as FTC in my US tax form. To me that makes sense, because I am paying taxes on it in Switzerland and DA-1 in the Swiss tax form does not work.