[6] On August 3 it was revealed that Yoo would make his acting debut in the web-drama Mischievous Detectives alongside Apink's Namjoo and fellow Produce 101 Contestant Ahn Hyung Seob.

Yoo played the role of Pyo Han Eum, an honorary forensic investigator that was awarded for solving a murder case.

[10] Yoo held his first fanmeet The Most Preferred Time on October 27 at the Woori Art Hall in Seoul's Olympic Park.

[13] Seonho was confirmed as part of variety show cast tvN's Nest Escape 2, with filming taking place in Greece.

[14] Yoo joined the cast of variety show Photo People 2 with filming taking place in Japan in March 2018.

[24] In 2021, Yoo joined JTBC drama Undercover, playing the son of Ji Jin-hee and Kim Hyun-joo, who has autism.

[27] The same year, Yoo became a fixed cast member of the KBS2 reality show 2 Days & 1 Night Season 4, with his first episode airing in December.