In 2026 IMO it's much better to use an LLM to keep 3 separate native front ends in sync than it is to try and use any sort of cross platform UI.
I have seen this suggestion several times recently regarding GUI framework threads on HN in the past week (There has been a surge!), but they are always described in the way you did: With no explanation of why. Just an assertion that native UI kits (of which you need a separate one for each OS family) are superior; cross-platform kids are an "inferior experience" etc. I have asked at 3 times and received no answer. I say this as someone who uses both Windows and Linux regularly, and find they are functionally equivalent once you have an application launched. There are ABI differences, driver differences, file system differences, etc which need to be smoothed over with feature gates for certain application functionality, if you're using certain functionality.
I want my applications to have the required functionality, run fast, and have a good UI. I don't care if the widgets look the same as on my other applications or the ones built in to the OS; this isn't even a thing because there is so little standardization broadly. Maybe on Macs it's standardized and cross-platform kits look out of place?
The proposed approach of "Use LLMs to vibe-code a system of 3 native kits" has cons to weigh. Or making your program Windows only or w/e for a look-and-feel reason or whatever it is has cons too. IMO all our OSes are so similar, PC software should almost all be cross-platform. Exceptions are mostly drivers and driver-adjacent code.
Speaking of which, my dream is an "HTML light" standard with a subset of functionality specifically designed for local UI use, ideally with lightweight non-browser engines supporting this standard shipping with all major OS platforms as shared system components.
We had browsers that ran on systems with 8 MB RAM, after all, and while it's not a fair comparison, there's no technical reason why a system with three orders of magnitude more RAM should struggle to run more than a handful of applications merely because they use HTML and JavaScript for rendering.
Though 8 MB RAM is a non-starter when a single RGBA texture @4k is ~30Mb and modern system often require 2 or 3 for buffering. Somewhere around the 60MB to 100MB mark seems to be the base for modern setups, at least on macOS.
New rule: Programmers with limited UI experience (that includes myself) should abstain from weighing in on what UI designers and programmers need.