You might have been unlucky searching for the a element that's really short. And very basic HTML would work everywhere.
But you might be more happy to go via the feature list: https://www.caniemail.com/features/
LOL ok that was just a really unfortunate coincidence. I used the <a> tag because I knew it would/should be supported everywhere so wanted to test the website with an input where I know what response to expect :)
When I enter "<a href="https://example.org>Test</a>" it says "No results found. Why not suggest this feature to be added?".
When I enter "<a>" I get "AMP for email", "BIMI", "accent-color" and lots of other CSS attributes starting with "a" as result.
When I enter "a" I get the same as above.
How do I check if I can email the HTML Anchor tag? The input says "HTML, CSS, ..." but it doesn't seem to understand HTML unless I'm doing it wrong?