Topfile.tj _best_ Here

?file=../../../flag.txt

And we see the contents of /etc/passwd (a standard test file for Linux servers), we know the traversal works.

Based on the search results, appears to be a website targeted by ad-blocking and content-filtering rules (specifically within ruadlist+easylist.txt and bitblock.txt ). Specifically, the filters target: topfile.tj###sliderbar : A slider bar element.