As Manjaro is a rolling release distribution, they do not release a new ISO often. You just need to install the ISO, then run an update when you boot in.
Example: 20.2 was released in Dec 2020, and 20.1 was released in Sept 2020.
If you want to install the newest and latest right off the bat, use Manjaro Architect. It pulls the latest ISO profiles, and installs packages that are currently in the repo at time of installation.