Updated to PHP 8 and menu will no longer sit under welcome area

I recently attempted to upgrade my php version to PHP 8. However, when I did so, the nav menu (which I currently have sitting underneath the welcome area on the homepage) moved to the top of the page, which causes some interesting issues.

I have had to go back to PHP 7.4, but I am aware that support for this ends next month. Is there a way to resolve this issue?

Thanks