What about Caddy, me and my friends have moved onto Caddy over a year ago and haven't experienced any issues.
The overall trend in WP hosting has been away from shared and VPS hosting towards managed hosts, who provide a WordPress-specific environment and do things like upgrade WP and plugins for you. As a result, I can’t imagine there’s a huge percentage of sites using Caddy.
(That said, even a small percentage will be millions of sites, since the WP install base is massive.)
Well, to name a few...
- Stripe (https://twitter.com/caddyserver/status/1559591673511813120)
- Mercedes-Benz (https://github.com/caddyserver/caddy/pull/5275#issuecomment-...)
- Approximated.app (https://dev.to/carterbryden/how-to-allow-end-user-custom-dom...)
- FusionAuth (https://fusionauth.io/blog/unlimited-domains-fusionauth)
The problem is those using Caddy are shy, not that it's not used at all. I know this because I see users removing the `server` header on the Caddy forum all the time, and many of the large users are just shy of their technology stack when it comes to Caddy.
Disclaimer: Member of the Caddy team