Although these two dramas possess distinct premises and storylines, there are certain similarities that cannot be overlooked.

Both dramas feature a cross-dressing female lead, which serves as a central plot device.
Both series revolve around a king with a troubled past, providing depth to the character and offering insight into the challenges they encounter.
Both dramas also incorporate scheming ministers, who contribute to the political machinations within the palace.
The tragic deaths of the female leads' fathers serve as a driving force in both series, giving rise to revenge and a thirst for justice. Additionally, both kings share a unique connection with the female leads' fathers.
The female lead in both dramas are wrongfully accused of crimes.
Palace politics play a significant role in both series, fueling tension and conflict.
Moreover, the second male lead in both series aims to marry the female lead, creating a distinct dynamic and adding an element of romance and competition.

While a "League of Nobleman" isn't a spy drama, it is a mystery drama. It also has a dark theme, good aesthetics and cinematography. It has some palace intrigue. It's a "Smart" drama like "My Journey to you". No romance though, story is bromance/friendship based. The ending wraps up pretty good.

Mature smart drama.
Similar scenario. ML trying to uncover past for revenge and clear fathers name. SML has a mysterious past that intertwines with ML's past. ML is a schemer and SML who helps ML is smart and upright.