How to check if the current page is at a specified path in the URL?

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You could try this instead

if (!is_front_page() && is_home()) {
    get_template_part('template-parts/blog-categories');
}

Explanation for the difference between front_page an home is here: https://wordpress.stackexchange.com/a/239838
if you set a page as a blog-page it is “home”, in your case the landing-page is the so called “front_page”. This is WordPress specific.