In February 2018, Liam Gallagher performed "Live Forever" at the Brit Awards as a tribute to the victims of the 2017 Manchester Arena attack, after Ariana Grande (whose show was the target of the attack) could not perform due to illness. In April, it was confirmed that he would support the Rolling Stones at The London Stadium on 22 May. Later that month, he confirmed that he had started work on his second solo album with Greg Kurstin and Andrew Wyatt. On 29 May 2019, Gallagher revealed that the album would be called Why Me? Why Not. On 7 June, "Shockwave" was released as the album's lead single. The same day, a documentary was released called As It Was, which chronicled Gallagher's return to music. On 27 June, Gallagher released another single titled "The River". On 26 July, he released a third single from the album, "Once", followed by a fourth single, "One of Us", on 15 August.
Liam Gallagher played an acoustic set for MTV Unplugged in Hull City Hall on 3 August, showcasing his solo songs. "Once" debuted live and new songs "One of Us", "Now That I've Found You" (which was inspired by Gallagher's reunion with his daughter Molly), "Gone", and "Why Me? Why Not." were played publicly for the first time. Liam Gallagher also performed several Oasis songs, including "Stand by Me" for the first time since 2001, and "Sad Song" which he had never performed live before. For the Oasis songs, Gallagher was joined on stage by former Oasis guitarist Paul "Bonehead" Arthurs. The special aired on 27 September, several hours after Why Me? Why Not. debuted at number one in the UK.
Why Me? Why Not. received mostly positive reviews from music critics. Many positive reviews complemented the album for expanding on the sound of As You Were, with Liam Gallagher's vocals also being singled out for praise. At Metacritic, which assigns a normalized rating out of 100 to reviews from mainstream publications, the album received a weighted average score of 74 based on 19 reviews, indicating "generally favorable reviews". In October, Liam Gallagher announced that the title of his upcoming third album would be Come On You Know. In November, he received the first Rock Icon award at the MTV Europe Music Awards. That same month, he announced that he would perform at Manchester's Heaton Park on 12 June 2020 and TRNSMT Festival on 11 July 2020.
On 31 January 2020, Liam Gallagher surprise released a live EP entitled Acoustic Sessions, which contained 7 live acoustic performances of both his solo and Oasis songs, as well as the original demo version of "Once". On 27 March, he announced that the Heaton Park show was cancelled due to the COVID-19 pandemic. In response to the pandemic, he announced that he would perform a free show for NHS staff at The O2 Arena on 29 October 2020. Later that year, Luiam Gallagher released his MTV Unplugged performance as his first live album, MTV Unplugged (Live At Hull City Hall), containing 10 of the 17 songs played. It was released on 12 June 2020 and debuted at number one on the UK charts upon its release, becoming Gallagher's third UK no.1 album as a solo artist.
On 27 November 2020, Liam released a stand-alone single titled "All You're Dreaming Of". The proceeds from the song go to Action for Children. Peaking at #24, it became his fourth solo single to reach the UK top 40, while also becoming the UK's highest selling vinyl single of 2020.
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