The answer to this question is really simple but before that, a few points:
Furthermore if compatible means working under 2019.3 then the first test should be to ensure proper compat values in the manifest, and only if they are in order source code could be investigated. So unless manifest states that add-on is compatible with 2019.3 further investigation makes no sense, and including is as compatible on the page in question simply confuses end users.
Which is a really nice and compact way of saying what I was trying to say in my last message. :)
