Glenn Howerton revealed during PaleyLive's panel for the 20th anniversary of 'It's Always Sunny in Philadelphia' that he almost quit the show in 2018. He said that at the time, being an actor, writer, producer and co-creator on the series made him feel like he was "boxed in" from pursuing other opportunities.
https://people.com/glenn-howerton-reveals-he-almost-quit-its-always-sun…