Now it's obvious, it's economic warfare, and a foreign power that creates an imbalance of this nature could be reasonably classified as an invasion.
Note, the US government doesn't "buy" companies, private citizens do. Yet, I would have no issues with private foreigners buying companies, I do think having a foreign government buying companies is very bad, especially if their leader is a dictator for life.
The threat is China demanding total payment at once (my vague understanding of the actual real world problem due to debt owed). Something that the US has laws protecting land and home owners [1], but no law says another country can't do this to us.
[0] https://en.wikipedia.org/wiki/Government_bond
[1] https://en.wikipedia.org/wiki/National_Housing_Act_of_1934
But espionage, market and currency manipulation, copyright and patent infringement and a miriad of other activities are illegal, yet China does them with impunity.
I can imagine they can demand whatever they want, (they are a sovereign nation) and can use that debt as a bargaining chip to be used in any negotiations.
In theory, I think you are correct, in practice, who know what is possible?
How does allowing the US to own Canadian companies harm Canada (economically)?
How does allowing the US to own French companies harm France (economically)?
How does allowing the US to own Nigerian companies harm Nigeria (economically)?
Buying a company is about the most legal way I can think of, for acquiring IP.
Again - how does allowing foreign ownership of companies in your country harm your country? You mention IP - but it's not your country's IP - it's a particular company's IP. If its owners want to sell it, why does it matter if they sell it to an American, or a Chinese investor?
Because there are second order benefits to Americans of America being the world power. (E.g., Americans really don’t want to live in a world where you have to learn Chinese to succeed in the business world, as opposed to everyone else having to learn English.)
The US management class has grown fearful of foreign owners. Because the foreign owners generally do not place Americans at the top levels because they can't trust them.
Maybe it becomes clearer by asking, "How does allowing China to own US companies harm the US (economically)?"