Navbar toggle icon

Hi there. I have a working site since 2019 and all of the sudden the navbar toggle icon is no longer visible. And the strangest thing is that if I replace the entire navbar with another one that works in a test page, it does’nt work either.
I’m stuck here. Can someone please enlighten me ?

Hello, have you already tested if the address for the icon is correct, if there is this icon, if the file has not changed its name?