Why did AC DC singer leave?

Can you elaborate on the reason why the lead singer of AC/DC, Brian Johnson, left the band? Was it a personal decision, a health issue, or perhaps a conflict with other band members? Fans are eager to know the specifics behind this significant change in the band's lineup, as his voice has been a defining characteristic of AC/DC's music for decades. It would be insightful to understand the circumstances that led to his departure and the impact it has had on the band and its fans.