What realm does the "sun god" in Taoist practice refer to?

It is the last realm you said. But the so-called final state you mentioned is by no means the highest state of monasticism, but the initial state of true enlightenment.

There is also a reason why we have reached that state. Because Buddhism accounts for a very large proportion in the whole universe, and there are many Buddhist gods, there may be an out-of-body experience of the Yuan God to reach the realm like Taoism, that is, the cultivated Buddha body comes out to move. Even if the realm of Yuan God is not very high, there will be no great danger, and there will be many Buddhist gods guarding it. The proportion of Taoism in the whole universe is much smaller than that of Buddhism, so it is necessary to reach a real state, so that Shen Yuan can have an out-of-body experience after the restoration. At that time, he can basically protect himself.

And what you said above is the realm of "practicing the Tao in vain", which is described by Buddhists, that is, the realm of Luohan's first fruit, that is, the realm of just realizing the Tao.

-Personal understanding, maybe there are exceptions, for reference only.