If you were a tax resident in Thailand in 2022, then you had previously deregistered as a tax resident in Germany, right? Why did you still have to pay taxes there?
To get a tax certificate in Thailand, you must have paid taxes in the year in question. When you submit your tax return you don't need to provide any proof, but of course the tax office can ask for proof later. However, I can't imagine that they will ask you for proof if you declare a very low income for tax purposes. Even if they do, it should not be difficult to prove such an income.
You can also submit a tax return in Thailand at a later date, but you may then be subject to interest and a penalty.