The Ubuntu Software package manager doesn't seem to help me do this... Chrome claims I have: Version 87.0.4280.88 (Official Build) (64-bit) and requires a "Relaunch" - but this fails. Actually it appears to succeed, but 15 minutes later it tells you it has not, and asks you to do it again.
After some investigation, I reckon the simplest answer is not to try to update, but to remove and then download the latest stable version from: https://www.google.com/chrome/
So, basically, don't follow instructions (especially from Chrome) to update, because that will take you down an endless stream of rabbit holes which will waste a lot of time an achieve very little. In my experience.
But I'm sure the command-line instructions here, which use the ppa for google-chrome-stable ->
How to install Google Chrome
...work fine.