> is LaTeX also falling out of use for technical papers?

In mechanical and aerospace engineering broadly, I see less use of LaTeX over time. It's hard to estimate precisely which percent of the market is LaTeX vs. Word vs. something else, but I think I can see trends. Almost no one where I work uses LaTeX, though LaTeX used to be more popular there.

I think it probably varies a lot by narrow specialty and publication venue too. Papers submitted to Journal of Fluid Mechanics seem to overwhelmingly use LaTeX. The main conference I would submit papers to during my PhD is primarily Word (though I used LaTeX). I have seen at least one Word-only engineering journal, though it wasn't something I would publish in.