It technically still exists in the game properties -> installed files tab, but it doesn’t really work. The backup files you get require you to be online to meaningfully restore and will trigger a patch to the latest game version.
Practically speaking it’s better to just make a copy of the game install directory manually, gives you a better chance of things working (even though most games require some kind of external tooling for that).
For current exports, it’s some custom .csm/.csd file combo. Not sure if there’s any tools for working with it, seems like it’d be more annoying than just using a normal archive format either way.