Yay, we're moving back to fat clients! What has been is what will be, and what was done is what will be done, there is nothing new under the sun.
If economics don't line up then you have to pull the plug and set them adrift, which is much easier and more secure with a fat client that runs without a server than say, a complex cloud system.
This sounds like the set up for a "No? Me neither." punchline. Certainly one of the features of Flash is that it gave you fairly good consistency across computers, but honestly my perception of Flash wasn't that it was going to solve some grand web problem, but more "oooh look, shiny rollover buttons!" and "ooh look, super obnoxious advertisement that forces people to pay attention to it!"
That's the interactivity aspect. At the time, it was the bees knees of UI capabilities.
A "native" electron or capacitor distribution system is a fine extension of a local-first web client. And an advantage of building fat clients generally is they lend themselves to such distribution models much easier than say, htmx or hotwire.
Native fat client have had their benefits and lots of people still prefer them, but always had the drawback of manual data management and installs. Being able to leverage any device you own with a cloud synced local-first client really gives you the best of both worlds.
But not all software fits readily within this model.
First, my list failed to include web because of the context. Web is, by far, the largest and most important platform. Even if I'm building only native installers for a project, I need to be able to build web projects with the same tools to make this work.
Java also fails "one code base" requirement as desktop and mobile are very different. The poor iOS support is going to cause it to fail the "square on" requirement as well.
No on Java.
Then we can write apps once and run them everywhere, desktop and mobile.