Not the OP, but I alternate between self-hosted instances of Outline (https://www.getoutline.com/) and Nextcloud (with Collabora) for this. Outline I actually like better than Google Docs for most things. Nextcloud is a little rough, but it has change tracking, which I need sometimes.
I’ve also seen a lot of people using Cryptpad recently, which I think wraps OnlyOffice.
I’ve also seen a lot of people using Cryptpad recently, which I think wraps OnlyOffice.