Huh. I have worked with Kubernetes so I guess it's possible that's a second place with client certs and I never noticed.

The big employers didn't use EAP-TLS with client certs. The University of course has Eduroam (for WiFi), and I guess in principle you could use client certs with Eduroam but that sounds like extra work with few benefits and I've never seen it from either the implementation side or the user side even though I've worked on or observed numerous Eduroam installs.

I checked install advice for my language (it might differ in other languages) and there's no sign that Eduroam thinks client certificates would be a good idea. Server certs are necessary to make this system work, and there's plenty of guidance on how to best obtain and renew these certificates e.g. does the Web PKI make sense for Eduroam or should you just busk it? But nothing about client certificates that I could see.