Late 90s. It was before Java got hotspot. Java prior to that was incredibly slow. Microsoft's J++ was a more performant runtime than Sun/Oracle java for several years. That ultimately became C#/.Net.
C++ had the benefit of running fast but it had all the problems you can still run into today. I'll never forget that app I worked on where function deep in the stack was returning a reference to a local string variable containing html...
Late 90s to early 2000s for sure. Tons and tons of backends of various kinds were written in it. If it was Windows it was typically running on COM/DCOM, and in UNIX it was usually CORBA. Sure, the UI was typically written in something else. Dawn of the Web with CGI, and if we are talking desktop people would use something like Visual Basic, Power Builder, or Delphi. But C++ pretty much dominated that space until Java got decent enough and fast enough.
Before Java, C++ was basically the only game in town for frontend and backend. There was always Visual Basic on Windows, and C, and a smattering of various pascal flavors.
When was that C++'s lunch? I might be wrong, but for backend dev(majority of enterprise work?) C++ was never a big thing.