From Frankfurt consulate almost impossible. I tried it several times, they are useless!
I spoke to a consular official I know personally for years. He told me that the difficulties of Germans being approved for visas and coe's is resulting from the treatment of the Thai King by the German government in 2019-20, who was residing in Germany at that time!
And what ties the hands of all Thai consulates in Germany is, that all visas and coe's have to be approved bei the royal Thai Embassy in Berlin!