Any modern browser supports a variety of custom resolutions, DPI, zoom, global font scaling, etc. Plugins can break CSS as well.
We've had two reports of this issue and despite testing by more than a dozen individuals, have been unable to reproduce. It's clearly an isolated issue.
Both elements, nav and container, have the same max-width with a flex wrap for x-small and x-large resolutions.
So, short of 99.99% of this community having faulty systems, it's safe to say it's not an issue with the site.