How to link to a page that can only be loaded inside iframe?

[Lamecode0]

Hello guys, I have a page constructed, it does not really have much content yet (more like nearly none at this moment). I decided the page content will always be loaded in iframe for a simple reason - I did not find a better solution to keep the menus available at all times at any page. Because if I make changes to the menu later, I would need to change it on all the pages. That simply does not look right to me. I am seriously just a beginner.

When I want to copy a link to a specific application, I can't, because everything is happening on the main page.
You can check what I mean yourself: http://lamecode.eu

When you come to the page, the iframe loads default.html into itself. Later, when you click a link in the menus, javascript loads different content into that same iframe on the index.html page.

I uploaded one sample application that I would want to link to, but the link is always on the index page due how the website works. 

Can you please suggest a solution to keep the menu on at all times, and when I make a change to the menu, it reflects on all pages? Because this way I cannot link to any of the future applications.
Another workaround could be somehow force the menus to pop up from some other file when I make the links standard, e.g. it will forward to specific html file that does not have menus embeddded inside them?
Thank you very much

Edited October 5, 2023 by Lamecode0