Pedro Sánchez is set to appear in the Congreso in relation to various cases of corruption. The exact nature of his involvement is not specified in the available information. Further details about the cases can be found through El País.

It is known that Sánchez's appearance is connected to corruption cases, but specific details are not provided here. For a comprehensive understanding of the situation, readers can refer to the original source, El País, which has more information on the corruption cases involving Pedro Sánchez and his upcoming appearance in the Congreso.