The phrase "leaner version" means a lighter or simplified version of something. It is often used to describe a product or an updated version that has fewer features, is more efficient, or takes up less space. Full definition
Of course, a clean inside meant that the phone was rocking a very lean version of Android. (androidauthority.com)
(Yes, I've seen the David Lean version... more than once.) (1morefilmblog.com)
The said item not only added 1,000 points, but also transformed Mario into a tall, lean version which might be a little creepy for some — you have been warned! (segmentnext.com)