In my limited experience, almost every language specific presentation at an HPC conference is about C++. New projects and initiatives like DPC++, SYCL/oneAPI, Ginkgo, etc are C++ based. And if you look at the open source libraries of the national laboratories, e.g. LLNL, C++ libraries are more common than C libraries, which in turn are more common than the Fortran libraries.

If anything I'd say that C++ is the default for HPC conferences.

That sounds right.

I wonder what the current split is. I'm not in HPC computing, but I see a lot of posts about how quickly Julia is being adopted.