LibreOffice has certified consultants you can hire[0] for large deployments, seems to be under pretty active development, and runs on Windows, macOS, and Linux, which together make up the vast majority of OSes used on the desktop. It’s been a while since I’ve used it heavily, but I can’t recall it being particularly unstable.

It doesn’t have professional support for individual users, I’ll grant you that.

[0] https://www.libreoffice.org/get-help/professional-support/