I want a good abstraction for building UIs that work on desktop and mobile without a bunch of manual configuration. Infinite Canvas and Spreadsheet work on both because the viewport is flexible, but that isn't true for forms or visual basic like widgety UIs. I am wondering if there is some research or another option that I do not know about.

I don't know of anything like that and would be interested to know if there's any. I guess some kind of hierarchical ui component tree where according to the viewport size more is "inlined" in the same view and the rest must be "navigated" in/out prev/next? that way you don't get the least common denominator problem

damn you were my main hope for knowing something

we are an industry that embraces least common denominators 😕

I have been trying facing down this issue in so many ways for the past few month and doing a lot of experiments.

You might look at the game industry, where you have Desktop AND Mobile versions of a game, where the designers have built dynamic UIs to fit into the two (or more) aspect-ratios/pixel-size screens. Sometimes this is just done via a complete new UI per-platform (brute force it), sometimes via auto-layout. (there is also the issue of dealing with 3 main input types, Mouse-n-Keyboard, Controller & Touch)...

My brother who works in games (highly biased perspective) told me that the bare minimum to port a game to any form factor is a "gamepad interface". Once your UI can be driven by a gamepad then it's accessible by default and you can add platform-specific niceties like keyboard input, mouse input, touch, etc. The UI building blocks in games are typically bespoke though. I only know imgui that's a little more standardized.

yeah the game format is often like infinite canvas. Main view (somewhat ok with different aspects) + (small) UI attached to the sides.