I would go for hedgedoc if the team can switch to markdown, otherwise Cryptpad to stay in an office-like suite.

If you already have nextcloud then that + collabora should be good enough. Otherwise installing the whole nextcloud suite just for collaborative editing seems like a lot imho.

Someone recently recommended me Textadept: https://orbitalquark.github.io/textadept/. Haven’t tried it on linux, and I am not really using it, but the interface is clean, it also has a CLI, and I thought I could give you another option :)