The official Chrome OS 77 Stable Channel is available for most supported Chromebooks, but unless you saw the notification for it on your device, you might not know about it. About Chromebooks 
Note Kevin's observation that Crostini updates upon first run. There is a thread about this on the Crostini subreddit .
Per the Release Matrix, it has been released for the Google Pixelbook. See Pixelbook Change Log
Did a scan of the Chrome OS sub-reddit and see one thread relating to this upgrade. Note the reference to touchpad update on the Pixelbook. I observe Touchpad firmware update and upon first boot Touchpad was not responsive. Subsequent reboot fixed the problem.
Scanned Crostini subreddit. Found a thread about hyperthread being disabled. Instructions for enabling hyperthreading are available here . Sounds to me like something to do if you don't like current performance, for me performance is not an issue.
I am currently running a Linux backup and it is acting like it is hung. Beginning to regret installing the Libre Office apps that increased the size of the container. The backup status flips back and forth between 9 and 10 minutes left, and I now got a System UI not responding message.
I think the problem is with the drive. I used another USB 3.1 drive connected via my docking station and it wrote at expected speeds.