Chromium removed support for generating TLS Client Certs within chrome in 2016 [0] and ever since then it has gotten harder and harder to use mTLS in Chrome/Chromium. Ten years ago it wasn't a great UX, but now it isn't even obvious how to use it. The impression I've gotten is that Chrome isn't interested mTLS.

[0]: https://groups.google.com/a/chromium.org/g/blink-dev/c/z_qEp...