@firebreathingduck
EtherPad, OnlyOffice, and a few other things support this kind of thing. It's not that there aren't F/OSS things that do it, it's that people are unconditionally recommending the one that doesn't.
EtherPad is a really interesting comparison because it does far less than LibreOffice, but it might do the thing that a specific set of users actually care about. And, if you understand what people are doing with it, then it's possible to recommend something that solves that problem. And it may even solve it better than the thing that they're using now.