He’s saying good looking GUIs are for plebian Mac users, you should use his vibeslopped TUI instead, like a real Linux user

Did you not read the part from the author saying that there is currently no linux support? And yes, it looked like a macOS app to me. [1]

But apart from given what I've seen from my experience with handling maildir, actually implementing mail sync, storage, and all the other things associated with mail AND calendar, it sounds risky to use a project this young.

https://news.ycombinator.com/item?id=49990805