The problem with your comparison with Taiwan is Taiwan is an island that is part of China but is currently controlled by an occupying force. This is agreed upon by almost all nations except for 12, the US also agrees on this btw.

What the west is saying is that regardless of this, China does not have the right to an armed resistance against Taiwan even though they consider it part of China. They even agreed to arm Taiwan to prevent this attack from happening.

So in terms of their statement on Palestine, this is actually consistent. The Palestinians have a right to kick out their occupiers, much like China has the right to kick out Taiwan's occupiers.

You view it differently, but as I stated before almost all members of the UN agree Taiwan is part of China.

*Edit: On a personal level I don't actually agree with this. I don't want an invasion of Taiwan. I'm merely pointing out the "gotcha" you tried to set up doesn't actually make sense. Instead it's actually quite consistent with China's position on Taiwan.

*Edit 2: This is also why China seems petty and runs around making sure all nations that trade with China state there's only one China. That's what the whole Lithuania thing was about. China is stating if the majority of the UN believes in a 2 party solution, then the Palestinians have a right to defend themselves. Since the majority of UN believes in a 1 party solution for Taiwan, then it's the Taiwanese who are the occupiers and China has a right to defend itself.

*Edit 3: Ironically, the same cannot be said for China's consistency on the SCS. If you wanted a "gotcha" then China's claim to the SCS is absurd. But that said, they never said it was OK for them to be in an armed conflict over that. So I guess take that how you will.