I feel like this is similar the conversations we heard about Rust and Go 5-10 years ago. late edit: 5-10 years ago people were complaining about these languages having issues binding databases, network protocols, etc.
Do Rust and Go have good (complete) Desktop UI libraries yet?
And probably never will. There are a bunch of projects but they are not very good or complete.
The problem is that "good" requires massive amounts of work that is beyond the capacity of single person / small team of volunteers i.e. typical open source project.
Which is why Flutter (and Electron) are the only reasonable technologies for desktop apps that I see today (and in the future).
They get majority of investment from other place: 99.99999% investment in Electron is investment in Chrome.
99% investment in Flutter Desktop is investment in Flutter Mobile.
Flutter Desktop and Electron will continue to benefit from massive investments in Chrome and Flutter Mobile. No other project building desktop UI can come anywhere close this level of investment.