What do you mean the site does not use an original product?
This site only runs Joomlart T4 template framework with template T4_bs5_blank.
All I did was making a copy of Template Styles T4_bs5_blank and set that copy as default.
Is there anything wrong with this method?
Even if I use the default template T4_bs5_blank. And activate that copied t4_bs5_blank template as default and then look at the mobile menu on my phone I don't see the arrows.