Can I claim deductions on foreign income that was taxed before moving to Germany

Hello,

This is my first year filing taxes in Germany. I arrived in Germany in May 2023 and was employed in Switzerland from January to April 2023, where my salary was tax-deducted at source.

As far as I understand, I need to include my Swiss income to calculate the effective tax rate on my German income. My questions regarding the foreign income are as follows:

1. For example, if my Swiss gross income is 28K for four months, of which there are standard deductions such as pension and unemployment contributions resulting in a net taxable salary of, let's say, 24K. Additionally, I have another tax deductable expenses that are acepted in Switzerland such as medical expenses,.commute expenses.

Could you please advise on the amount (28k or 24k or 22k) I should declare here that will be used to calculate the tax rate on the German income ?

Thanks