Update: At this time the errors are no longer being reported, indicating the report now considers canonical tags or uses only indexed pages.
This is a simple test to see if the duplicate title tags and duplicate meta descriptions report takes into account the canonical tag.
The following links enable Google to crawl different URLs for this page. Each URL contains exactly the same content, including a canonical tag to this page.
Let's see if the Google Search Consoles HTML Improvements report lists these URLs as duplicates.
About three weeks later one of the test links showed up in the duplicate report, indicating the canonical tag did no have any effect.