History happened

LOL. So insightful. History is constructed and exists in the present.

They are now independent of mainland China

No, they aren't. They are completely dependent on mainland China. Oh you meant politically? So was Hong Kong. You know why? Because the British colonized it. Does that give it legitimate claim to being separate? No. In Taiwan, the British and US didn't colonize it, they propped up a puppet regime and made it a neo-colony, fully dependent on the West for military and political life, fully dependent on the West and now China for its economic life. Taiwan can, in no reasonable framing, be considered "independent" of anyone.

They own that island

That's not how private property works. I would expect a capitalist bootlicker to understand the basics of private property.

They live there, they take care of it, they decide how it’s run

They literally ran a terror campaign for 40+ years! They committed mass murders of people who disagreed with them. And they operate the island as a proxy of Western imperialists!

Forcing your will on others is clearly a bad thing. The fact autonomy upsets you should be a moment of realization to self reflect on your trash values.

This is why China isn't going to invade and occupy. Unlike the West, China understands that this is an unsustainable path towards integration. What they will do is keep pushing the imperialist powers out of the region and continue to develop their economy, their political system, and their diplomacy. They will continue to disrupt Western spy networks, Western propaganda networks, and Western influence campaigns. And through soft power, they will create the conditions for Taiwan to reintegrate.

What you don't understand is that failure to reintegrate means war with the West. The West wants to fight China but not directly. They will gladly create security problems for China via Taiwan and they will gladly indoctrinate Taiwan and create conditions for Taiwan to get involved in a hot war with China. The US will fight China to the last Taiwanese, just as they have done in every proxy war. China doesn't want that. It considers the people of Taiwan to be their family. They want their family to live and thrive. And they understand that the West will kill every last one of them.

The fact that you see nothing wrong with the continuous centuries of European imperialism creating violent strife everywhere they operate, threatening to escalate to nuclear conflagration, and operating 600 military bases around the world in order to impose their will on literally all of the world's people should be a moment of realization to self reflect on your trash values.