[Apreche]

Depending on your application, write as much of the core functionality as possible into a cross platform library and/or server in your language of choice. Expose all functionality through a strong API.

Now you can build completely native GUIs in the appropriate language for each platform. Start with the platform which will likely have the most users for the application. Bonus if the application is open source, other developers will build all kinds of native GUIs for you. Just look at how many GUIs are out there for things like PostgreSQL, Git, IRC, etc.

I know this doesn't exactly meet your requirements, but I think this is the way to go if starting something in August 2022.