When typing in the names of the text files explicitly we can read them.

When trying ././././

We get an unauthorized message to appear.😔

We know that it is traversing the directory tree but correctly
Now we need to find a way to bypass the /usr/ forbidden path
Lets try ..
with the flag.txt
FLAG

It works we are able to get the flag

💡
picoCTF{7h3_p47h_70_5ucc355_6db46514}