Let’s enter the challenge: The message says:

There is a way to bypass the main activity and invoke other activities that are exported.

I searched for activities I can export, using looking inside AndoridManifest.xml, and check if the activity has the attribute exported=true or has intent-filter.

We can find several activities, however, the one that dragged my attention is b25lActivity:

and this is the source code:

We need to create explicit intent with this activity:

adb shell am start -n "b3nac.injuredandroid/.b25lActivity"

So, the second flag is S3cOnd_F1ag.