I maintain a C++ service running in production since 2015. I released Windows and Mac kernel drivers in 2012, both of which are still used in commercial products. My NAS runs a patched kernel because the stock dm-cache didn't offload burst writes onto SSD. I once built a virtual filesystem driver to run inside my PS2 so that I could exfiltrate in-game debug data over LAN. My most recent low-level project was PCB+Firmware for a digital camera.
But:
Ruby on Rails just has a much better bang for buck than C++ and customers know it. Powerful hardware is dirt-cheap these days, so nobody wants to pay for the extra +50% you get from C++ over JavaScript.
And if you want to be paid well, call your multi-threaded C++ calculations something like "CPU-accelerated AI deployment optimization" ;)
And lastly: Most embedded C/C++ jobs went to China! We used to design hardware and firmware in the west. But nowadays, you just book a Shenzhen shop to design, code, and produce your product. That's why nowadays almost every device has firmware with Chinese debug strings inside ^_^