Kind of a half-assed estimate but summing up web/mobile vs everything else (excluding QA) from the counts from this article https://learning.linkedin.com/blog/tech-tips/the-american-ci... gives us about 13% of software jobs being non-web. I lump in mobile with web since a lot of mobile apps are cross platform hybrid apps using web stuff.

Personally, I think even that estimate is too high; I'd be surprised if the true number wasn't somewhere closer to 5%.