Nextcloud is a steaming pile of barely maintained donkey dung one should not approach with anything other than a 10' pole while wearing a full Hazmat suit.

What are its cons? I used it years back and worked fine; did it transition to the dark side or it's a matter of bugs? I'd use it only self hosted of course. Alternatives?

I use it at home just fine. Granted, I only use it for files and I’m not using the office apps from it.