I am aware of the python chess and chesslink mchess work but would like to attempt to interface it with lichess.org. My purpose would be to play others on lichess using my Millenium board. The API's I've found for lichess seem to be for a chess engine interface rather than external hardware. Any guidelines on where to find other similar work (like how DGT may do it)?
As you've seen, the Lichess API only allows bots to use the API functions that make moves in an ongoing game. As far as I can tell, this is intentional; the API requires that anything that can generate moves in a game by some means other than human interaction on the Lichess site must be flagged as a bot.
Which means (again, as far as I can tell...), the only way to do what you want to do would be to create some kind of intermediary between the e-board and Lichess that actually mimics the actions a human would take during a game (such as simulating mouse clicking and movement on a game's web page).
I personally would not know where to start if I were trying to do this, and I also don't know if doing something like this would trip Lichess's anti-cheating detection in any way. But it appears that this is what you'd have to do in order to play on Lichess using an e-board.