He says, what is the ruling on shaking hands when entering the diwaniya? Should I greet from afar and sit down, or should I shake hands with everyone?

Because some people say shaking hands is a bid'a. No, it is not a bid'a.

It is not said that shaking hands is a bid'a. When two believers shake hands, their sins fall away as the leaves fall from a tree.

But the habit of the Prophet ﷺ with his sahaba every day, when they met the Prophet ﷺ, the one who came to the gathering would sit where the gathering ended for him.

He would not shake hands with everyone, but if you do shake hands, there is no problem.

If you shake hands, there is no problem, and if you do not, that is better, but it should not be said that shaking hands.

It is an innovation, and Allah knows best.