I do not see any option to log out of all devices.
I recently logged in to the Zwift app on a friend’s computer. After running Zwift I did not see any way to log back out, so I changed my password as a security measure. When I got home I found that I was still logged in to all of my devices under the old password. I was allowed access to my profile: in the Zwift app on my computer, AppleTV and Android; in the Companion App on my Android; to the forums online on my computer and Android; and to my.zwift.com on my computer. All because I had logged in previously with the old password. It appears that until I actively log out of each app on each device I will not be asked to enter the new password to access my profile. It seems to me that changing my password should immediately cause all apps on all devices to log out of my profile and require a new login. At the very least some means of logging out of all devices should be provided.