Thank you very much for doing the test for all of us. It is good to know that Kinvoc may not be work, at least not right out of the box without any tinkering.
I guess the safe bet would be office joycon + egress grip case then for my case
I think steamOS now has a toggle for combing as one for the first party controller, see here
I am interested to see if this is available for third party. Well, as long as a pair can be used as one it is great. Third parties’ have better grip and they allow better posture when gaming