What you said above has been my experience as well. I have been pasting the internal link into an existing note so go to "edit" and copy/paste the evernote:/// link into other applications (namely airtable). Inconvenient but it does work. The issue I am having is that when I click the link in Airtable to open a specific note in the Evernote app, it tends to open either a random note or the most recently edited note. Often these notes are not even in the same notebook as the linked note.
I am a new Evernote user and have never used the legacy or classic version, only the most recent version starting 10/13, so cannot speak as to whether legacy links work
