What can readers infer from this sentence?
For nearly 100 years, the Girl Scouts and their supporters have made their annual cookie sale into an iconic American tradition—and all while they learned valuable life lessons, made their communities better, and most of all: had fun.

The sentence states that the Girl Scouts and their supporters have made their annual cookie sale into an iconic American tradition while learning valuable life lessons, making their communities better, and having fun. This implies that selling Girl Scout cookies involves hard work and effort, but the rewards include the valuable life lessons learned, community impact, and enjoyment experienced by the participants.