Completely opposite experience for me.
I love working with Dart (which IMO is _not_ "worst parts of Java and Javascript (...) turned (...) into a language", "Terrible to write, terrible to read, terrible to use" - quite the opposite, actually) and its toolchain, including Flutter.
I find the architecture simple to follow, no need for "either print apps as fast as possible or to emulate some Clean Code like behavior", though I do think some people use overcomplicated state management solutions. But nobody forces anybody to do that.
My experience with Web has been fine so far and I've seen fully cross platform Flutter apps working absolutely fine on mobile, desktop and web.
This is not to gaslight your experience, YMMV after all.
And React Native, with its dependency hell, project rot, npm ecosystem under the hood, and transpilation with lax runtime leaking into TS, is a total no-go for me. Though I base this opinion partially on my experience with NodeJS, and partially on that of my friends who use RN.
Btw. Does your platform support bundling UI in addition to streaming it from the server? How large is the bundled runtime?
PS. Clicking on "see all supported platforms →" on your project's homepage gives 404 for https://docs.hypen.space/docs/adapters .