In August 2020, while many parts of the country were still under major restrictions related to the Covid-19 pandemic, Smash Mouth appeared at the Sturgis Motorcycle Rally, a huge annual event in South Dakota, and performed before thousands of fans — very few of whom, according to reports and videos of the event, were wearing masks or taking any precautions.

Mr. Harwell drew cheers from the crowd — but wide condemnation elsewhere — when he said from the stage, “We’re all here together tonight, and we’re being human once again,” and made a crude dismissal of the viral threat.

In 2021, Mr. Harwell left the band and retired from performing after a live show in upstate New York during which he was seen slurring his words, using profanity and apparently giving a Nazi salute.

“I’ve tried so hard to power through my physical and mental health issues, and to play in front of you one last time, but I just wasn’t able to,” he said in a statement at the time.

He is survived by his fiancée, Annette Jones; a brother, Mark; and three sisters, Carla Crocker, Michelle Baroni and Julie Harwell.

In 2022, Smash Mouth recruited a new lead singer, Zach Goode, and the group has concerts scheduled in coming weeks, including one on Thursday in Madera, Calif. Mr. Hayes, the manager, said the band was still scheduled to perform there.

In a statement on Monday, Mr. Goode said: “I love singing these songs every night and carrying on the spirit of rock n roll in front of the best fans in the world. I will continue to try, in my own way, to honor what Steve and the band have created.”