This issue has been around for a while, but I didn't see it listed so thought I'd send a ping. Pardon if it has been raised elsewhere. I have duplicated this on 1.78 and 1.93, don't recall if it was an issue before but I believe it was.
Setup:
In main window select View -> Select Sidebar Computer selection checkbox.
In main window, computers will be listed, but column width may truncate longer computer names.
Attempting to adjust column width interacts with adjusting width of entire window, and results in Computer selection sidebar disappearing entirely. At that point, it is impossible to get the column back.
Closing the main window and reopening it will not restore the missing column. It is necessary to quit entirely and restart to get the column back and, again it will not be able to be adjusted in width.
If you want to enlarge the Computer sidebar, once you see the two arrows click.
The window itself is now enlarged, but the border stays.
Now drag the border with the two arrows where you want it, larger or smaller.
Release the mouse button and you are set.
If the sidebar is still too small, repeat.
It's not optimal, but it's really complicated to change, for something you do maybe only once.
Values are probably stored when you do File Exit, or immediately, I'm not sure.