Modern browsers do fail on ACID tests anyway. display:flex broke old box model.

> one can share the millions of frameworks ...

For your *desktop* application you need just one, not millions of them.

> libraries and muscle memory

Not a problem, here I am using Remarkable [1] as it is: https://github.com/c-smile/sciter-js-sdk/tree/main/samples/m..., in other places I may use LeafletJS for showing maps, etc. Essentially all libraries for JS/NodeJS should work out of box.

Problem is that desktop UI has different UI model from a web page. Web page / Web app is usually "endless paper tape" opened full screen - has defined width but no height - no need for vertical alignment for example.

And desktop UI is usually different - small or vertically and horizontally space limited windows, etc.

In Sciter you can show element as popup one - in separate window that can be rendered outside of your [small] app window, consider this popup: https://sciter.com/wp-content/uploads/2021/02/select-table.p... , good luck with recreating this in browser. By the way that <select> element is defined as:

   <select>
        <tr role=option value="1">
            <td>Option 1</td>
            <td>*Short*</td>
            <td>123456</td>
        </tr>
        <tr role=option value="2">
            <td>Option 2</td>
            <td>******* LOONG ********</td>
            <td>123456</td>
        </tr>
        <tr role=option value="3">
            <td>Option 3</td>
            <td>*Short*</td>
            <td>123456</td>
        </tr>
   </select>

Sciter supports arbitrary markup in selects, popups, etc. No one of "millions of frameworks" will help you with that.

Also this

   <frameset cols="200px,*">
     <section>A</section>
     <section>B</section>
   </frameset>

will give you split-view out-of-the-box. But web dev's will start looking for frameworks in order to achieve this simple component that browser have internally.

TL;DR: Web and desktop UIs use inherently different models. You can share parts between these two different platforms but only parts, really.

[1] Remarkable JS: https://github.com/jonschlinkert/remarkable