For a project as big and old and full of legacy code as LibreOffice, I think their interface is pretty great. And its way more customizable than MS Office. Its just not the absolute latest and greatest in styling.
And, if MS didn’t make it so hard to maintain compatibility with their “open” file format, TDF might be able to put more resources into UX. As it is, they have to reverse engineer all the nonconforming BS that Microsoft puts in their OOXML implementation.
Have you considered using a mesh VPN instead of opening a port to the public? Nebula and TailScale are both great options that have a free tier which is more than enough for most home use cases. With Nebula you can even selfhost your discovery node so nothing is cloud-based, but then you’re back to opening firewall ports again.
Anyway, its going to be more secure than even a properly configured reverse proxy setup and way less hassle.