As of Evernote 10.2.4 and almost 2021 this is still broken. Pressing TAB inserts four spaces instead of the TAB character. WHY EVERNOTE? WHY, WHY, WHY? It's been 6 (SIX!) years since this was first reported. This is basic text formatting. Even TextEdit.app or notepad.exe can do this, why can't you?
What is even more mind boggling is that if you press TAB at the beginning of a line it works perfectly fine but if you do it let's say after typing a word or a character it inserts four whitespaces. This is so confusing.
I ended my premium subscription with Evernote because of the focus on advanced features and constantly replacing the app/s with "a new layout" rather than focussing on basic functionality.
A disgruntled Evernote user.