[18] During Astro's second Astroad to Seoul "Starlight" concert which was held on December 22–23, 2018, Rocky performed his first solo song "Have a Good Day".

[20] In 2019, Rocky self-composed one of the tracks from Astro's sixth EP, Blue Flame, titled "When the Wind Blows".

[27] On September 29, 2020, Rocky's first OST entitled "Shiny Blue" was released for the web series Dok Go Bin Is Updating.

[29][30] Rocky appeared as a competitor named 'Undutiful Child Cries' in MBC King of Mask Singer on its 305th and 306th episode which aired on May 2 and May 9, 2021, respectively.

[32][33] Rocky was credited as a lyricist and composer for "7Days Tension"—a promotional single by the girl group Weeekly which was released on May 28, 2021, for the eyewear brand Davich.

[34][35] On October 14, 2021, Fantagio confirmed that Rocky was cast in the web drama Hyangjeon of Youth, based on the South Korean classic literature 'The Story of Chunhyang'.

[36] On October 28, 2021, Rocky was announced as part of G-Market's mystery romance thriller web drama called Find Me If You Can.

[41] On March 28, it was reported that Rocky would sing the national anthem for the opening games of the 22nd Season of the KBO League happening on April 2, 2022, at the Changwon NC Park.

[42] On May 16, Rocky's solo ballad song "S#1" was released as part of Astro's third full studio album — Drive to the Starry Road.

On May 29, G-Market released a teaser for its new web series called X: SSG where Rocky played the role of "Woo-ju" together with his bandmate Jinjin, Monsta X Hyungwon, Minhyuk, Joohoney, AB6IX Daehwi, Jeon Woong, and Apink Yoon Bo-mi.

[49][50] Rocky participated in writing, composing, and choreographing his brother's band's debut song called "Wanna Be Love", which was released on February 23, 2023.

[57] On November 22, Rocky released digital single music video "On My Mind" to celebrate the first anniversary of his solo debut.