The best sources are industry studies by market research companies that collect information from companies. The best public sources, IMO, are those based on job openings (as jobs correlate more with total number of lines of code than sources based on number of repos, PRs, or questions). Some of these are about a year out-of-date:

https://www.devjobsscanner.com/blog/top-8-most-demanded-prog...

https://uk.indeed.com/career-advice/career-development/codin...

https://www.itransition.com/developers/in-demand-programming...

https://www.hackerrank.com/blog/top-developer-skills-in-2025...

Viewing these numbers through an optimistic or pessimistic lens is a matter of perspective and, of course, no one knows the future. But when you compare Rust, which is a middle-aged language now, to how languages that ended up "making it" were at the same age, the comparison is not favourable.