As you have learned already, CBL is based on Challenges.
Wastelines project consortium has designed a series of WebQuests and Digital Breakouts. All these educational resources includes Challenges for your students. (Re)visit these resources at https://wastelines.eu/
Mastering the CBL approach and the ability top design CBL-based lesson plan, it will make easy to you to incorporate Challenges in the form of Wastelines WebQuests and Digital Breakouts.