I'm actually a great fan of flutter and imo it is the best cross-platform solution out there. Probably except for web: though it produces very good result performance-wise, the end result is never really "web" and doesn't act like traditional web. As for desktop applications(whether it be windows, linux or mac), it seems like it's too mobile-oriented. I see great potential for simple solutions like self-service opera…
On the web it's DOA for most use cases - it's just a canvas, so scrolling, text selection, shadow rendering, etc. is custom, doesn't feel native and must be downloaded and compiled.
It can have a future on desktop. One "cultural" obstacle is that the de facto default widget system is Material, which is simply a wrong approach to desktop UI.