Check if I am in the Admin Panel (wp-admin)?

I want to have my plugin check if the user is anywhere in the Admin Panel (wp-admin) before executing a script. This would include:

/wp-admin/
/wp-admin/edit.php?post_type=page
/wp-admin/themes.php
etc.

Similar to using the using the global $pagenow:

global $pagenow;
if ( $pagenow == 'upload.php' ) {
    # do something if in the Media page
}

From doing some research, it looks like the get_current_screen() function is something I need, but this is what I’ve come up which doesn’t work:

global $my_admin_page;
$screen = get_current_screen();
if ( $screen->id = $my_admin_page ) {
    return $content;
}

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