Users of the Canary version of Microsoft Edge Chromium have recently reported issues with the installation of add-ons.
The problem has since been successfully pinpointed to the built-in Antivirus software.
The virus check function has been found to block add-ons from being installed in the latest version of Canary. Add-ons from the Chrome Store seem to be exempt from the problem, though.
Canary is updated every night, so minor problems are usually fixed very quickly.
You can download the Microsoft Edge Insider Channels here.