What font did the ancient ministers use to write the throne for the emperor?

Generally use "Cao Zhang".

Please refer to the following:

"Cursive script", also known as "broken grass" and "modern grass", consists of seal script, eight points and chapter grass, and follows a variety of ancient characters. The cursive script originated in Cao Zhang, and Cao Zhang has a strong taste of official script, so it is named because it is mostly used for memorials. Cao Zhang has further developed into a "modern grass", also known as a "book". Today's cursive script is mostly simpler than Cao Zhang's and running script. The cursive script gives the viewer a bold and fluent feeling.