backup – Where does Google Drive File Stream store offline files and folders?

I use Google Drive File Stream for work, and there are certain mission-critical files that I need available for offline access. File Stream makes this easy: control-click on the file, and choose “Available Offline”. Great!

But where are these files stored? With the “old” Google Drive (now “Backup & Sync”) there was a Google Drive folder at the top of my user directory; this folder was always available, whether Backup & Sync was running or not, and Time Machine would back it up for me (if I wanted it to). With File Stream, I have no idea where those files are — when the program is not running the “Google Drive” volume unmounts from my system, and the files appear to be completely inaccessible; moreover I don’t think Time Machine backs them up.

Where is File Stream storing these offline files? Is there a way to back them up, or to access them when the program is not running?

Just for clarity’s sake: I am interested in the answers to these questions on MacOS, specifically in Catalina, if that makes a difference.