I'm experiencing the same graphical corruption.
My Specs are almost identical.
Distribution: Ubuntu 19.04
SteamVR version: 1.8.6
Steam client version: Sep 23 2019,at 16:07:56
Opted into Steam client beta?: Yes
Graphics driver version: Nvidia 435.21
I've seen similar behavior.
Sometimes the dashboard just won't show up, and sometimes it does but is distorted in weird ways.
https://gist.github.com/Goofybud16/cc14f06b748826913e970d8ec1eb486c
Same here, similar specs (mint instead of ubuntu)
Display of ipd adjustment is also corrupted, if I had to guess looks like the stride/texture format is wrong when handing off to the compositor.
(Sadly can't get a screenshot of that, vr view isn't working for me either)
I experience this issue exclusively in the SteamVR beta, but not in the stable version.
System information: https://pastebin.com/Q8ch0JER
Hello, per "Fixed Dashboard and IPD slider being corrupted on Nvidia drivers" in the SteamVR 1.8.8 beta update, please retest this issue.
Dashboard and IPD issues working for me now (Nice IPD update, also doesn't stay visible for 30 odd seconds any more)

the dashboard works for me again
Nothing extracted yet.
Describe the bug
The dashboard is torn or distorted. This makes it really not possible to use the dashboard.
To Reproduce
Steps to reproduce the behavior:
Expected behavior
The dashboard should not be distorted
System Information:
https://gist.github.com/fabiankranewitter/a5b1e9769b70ca7e84337a5fa8b48969
Screenshots

Note: Commenters who are also experiencing this issue are encouraged to include the "System Information" section in their replies.