As much as I love free software, LibreOffice interface feels old and ugly (to me, at least). It would be nice if there was more focus on the UX/UI design in open source projects. Of course, most programmers are not UX/UI designers, and designers don't tend to work for free on open source projects.
No... the problem with desktop software is that creating a good UI/UX is a hard software problem typically solved by software developers instead of designers. Whereas, the accessibility and power of web technologies show that making UI/UX an easier software problem (HTML, CSS, JS) automatically attracts more designers yielding better UX/UI.
I find this a bit questionable. What are some examples of this good UX and UI? Many HTML-ish UIs I can think of are not good. Slack, Discord, modern Windows apps such as the new settings app for example. They tend to suffer from poor reimplementations of native widget functionality, poor implementations of scrollable elements especially infinitely scrollable ones, low information density and too much whitespace often exacerbated by flat design, janky responsiveness often with high latency.