Is there no way to close Raft after opening it?

Once enabled, Raft cannot be disabled on your cluster. The cluster nodes will fail to restart if you remove the Raft feature.

Why can’t it close?

If I really want to close Raft now, can I do so by deleting some table information from the system’s record Raft?

I don’t think so and it was never tested.
Why would you want to turn it off?

We are in the process of using Raft for more and more things. Starting with ScyllaDB 5.2, Raft is mandatory to use, especially if you want to benefit from the improvements we developed on top of it.
So I don’t recommend trying to turn it off, instead please report any problems you experience related to it.