I do not understand where you see the problem? You share a calendar(with a task list) just as every other thing in nextcloud. It has always been that way for years now.
Just as I said you can grant read or write acccess to the Users you are sharing with.
Of course this is exactly what phatair asked for as he even repeated that he just wants to edit shared tasks with different people. And this feature is working for years now in the Webapp and even on Android as I discribed it.
Well this even was discribed back in 2019 in the same forum: How to share the Task App with others? - #12 by dosch