Legato is a simply a playing style. It does'nt tell about a certain thing shall happen, when you play legato, like you seem to think.
What do you exspect to happen, when you play legato? If there was a Playmode named "Legato", then what would you exspect to happen, when that was choosen?
We allready covered the Legato option for the Lag generator. And the Lag generator is used to create Portamento in Matrix 12.
Are you sure you are not talking about trigger/ retrigger, when you say legato? And if so, what to trigger/ retrigger?
Please keep in mind, that you have quite detailed options for many things in Matrix 12, that many other synths does'nt have.
Perhaps it's because you read about the wrong things in the manual, that you can't find informations. It can be a good idea to read the full manual, especially when a synth have many possibilities. You might even be inspired and learn about things, that you never have heard about or understood before. This informations can perhaps also be useful to understand other synths.
Matrix 12 V2 also have build in tutorials that among other things cover the advanced panels.
I'm not saying that the manual could'nt be better, but there are descriptions of the parameters.
Beside that, then sometimes you also have to spend some time to exsperiment to understand it and/ or get a feeling about what happens.
That's why i encourage to study and to exsperiment. This also will lead to learning by doing.
Feel free to ask further. But please be more detailed and describe the functionality you are looking for.