Our general purpose departmental web server has supported HTTP/2 for a while. When we added HTTP/2 support it was basically because it was there; HTTP/2 was the new and shiny thing, our Apache configuration could support it, and so it seemed like a friendly gesture to turn HTTP/2 on. Until now, I've never looked at the statistics for how many HTTP requests use HTTP/2 and how many use other HTTP versions.
Our general purpose web server supports both HTTP access and HTTPS access, unless people opt to forcefully redirect their own pages from one to the other ( we have plenty of old pages with mixed content problems, so we can't do such a redirection globally ). However, these days that may not be much of an issue and browsers may force HTTPS on the initial connection, which will succeed with our server. I mention all of this because unfortunately our logs don't let me see how many requests are HTTP versus HTTPS. In some environments I could assume that all HTTP/2.0 requests were HTTPS, but the standard Ubuntu Apache HTTP/2 configuration enables h2c so I believe we can do HTTP/2.0 over HTTP connections without any sign of this in our current logs.
The overall number is that about 55% of the requests are HTTP/2.0 and all but a tiny trace of the remaining 45% are HTTP/1.1. However, this isn't uniform. For instance, we've somehow become a load bearing source of commonly used ML training data , and requests for this data are about 70% HTTP/2.0. Meanwhile, a URL hierarchy that maps to our anonymous FTP area sees much less activity, probably much of it from automated crawlers, and only 21% of the requests were HTTP/2.0.
If I look at the claimed User-Agents for HTTP/1.1 requests, some things jump out. A lot of requests come from 'pytorch/vision', along with 'GoogleOther', GPTBot, something claiming to be Chrome 83, PetalBot, Applebot, no User-Agent at all, Scrapy, and a whole menagerie of other crawlers. Actual probably authentic browser user agent values are mostly absent, which isn't a really big surprise since I think browsers aggressively do HTTP/2.0 these days.
(A lot of those 'pytorch/vision' requests were for that commonly used ML training data , but they seem to have been dwarfed by the HTTP/2.0 requests from browsers.)
Given even this cursory log analysis, I suspect that for our web server, HTTP/1.1 requests are significantly correlated with access from non-browsers, including crawlers (both overt and covert). Again this isn't really a surprise if modern browsers are trying to use HTTP/2 as much as possible, since most people are running modern browsers (especially Chrome).