I am moving from Drupal 7 to SilverStripe and find a number of differences that might potentially impact my new SS site.

Other CMS systems like Joomla, Drupal, and WordPress all have a method by which they scan installed modules and report which modules are superseded by later versions and offer update opportunities.

I do not find such a mechanism in SilverStripe. Maybe I am missing something as a new user.

Is there a add-on to the CMS that scans all the installed modules in the SS install path and compares the installed to what is available from the add-ons, themes, etc. for updates?

This would both simplify the update process and assure that the site remains up to date.... or
Do I have to manually check the git repository and do the laborious comparison myself?

If you are using composer to install your modules, you can run the command in terminal "composer show -i" which will display all currently installed modules and their versions. If you want to see if there are any available updates (which out actually updating them), use "composer update --dry-run". There isn't a module that I'm aware of that does this specifically, however composer is a great tool and worth learning more about. Possible that someone could write a GUI module for composer you could run locally.

Well unfortunately my shared facility hosting service does not allow the use of composer. I must use the download->unzip->upload method. This is the reason I am on this quest.

This would be a very welcome and useful module / feature for SilverStripe administrators who cannot rely on composer for this information.