The CSS is coming from Send In Blue – not something you can edit as its coming from another server. You may want to report it to them as its bad practice for them to install very generic CSS – it should be specific to their code requirements
Try adding this CSS to overwrite it:
.main-navigation ul.menu {
border: none;
padding: 0;
width: unset;
max-width: unset;
}
Not required now but in regards to disabling Elementor – you won’t lose anything by disabling it and re-enabling it.