How to check if current static page is frontpage from admin plugin

This is why I asked for more code context. I’ll have to guess that you are checking for the front page outside of any hooked function, or inside a function that is called too early, before is_front_page() is ready.

The following will work.

function your_function()  {
$d = is_front_page();
var_dump($d);
}

add_action( 'wp', 'your_function' );