Mint 19.1 has moved the allow desktop sharing setting (amongst others) from it's own menu item to the dbconf Editor.

In xfce, and maybe all distributions, this is just a theory - the "allow sharing" setting does not exist. Other settings do; but not sharing.

The Mint 19.1 update documents do not mention this major change to using dbconf Editor!

I assume it's supposed to be in org.gnome.Vino .

No vino is not automatically installed. Installing vino does not help - it just gives settings to look at.

Myself, I use nomachine for connections - which works from Mint 19.1 to Mint 19; but not from Mint 19 to Mint 19.1 - so it's all in Mint 19.1 not allowing desktop sharing.

I am not using Mint 19.1 currently so I could be wrong, but I think you mistake "does not include automatically" for "does not allow". It DOES allow desktop sharing, it is just not as easy and obvious as you expect. Perhaps if you pursue the "how to" on the Mint Forums at https://forums.linuxmint.com/

It looks to me as if you are not the only one with the question, and there are many comments, suggestions, and a few answers.

Yes there are lot's of answers in forums, etc. Many many answers and examples. But they are all for other distributions or earlier versions of Linux Mint.

I am bleeding edge writing about Mint 19.1 and it's undocumented and unmentioned move of Desktop Sharing from the Menu to dbconf Editor; dbconf Editor does not display the allow setting because Vino does not have the allow setting.

gsettings list-keys org.gnome.Vino

Ah well ...

SOLVED

My upgrade was on top of Mint 19

I'm guessing some setting was replaced, or not replaced, I don't remember my reply when asked.

The solution is Mint simple.

Use Synaptic and remove NoMachine completely.

Download and install the latest version.

You misunderstand. I was examining the ones that specifically mention Mint 19.1. And that forum is ONLY about Mint, no other distributions. Did you even look?