Not just governments but any centralized entity should not own a large amount of bitcoin which includes all these "investment companies" that have been growing like mushrooms. They all can affect the Bitcoin world in a negative way, some more than others like governments.
At least in the case of spot ETFs the situation is a bit different as the Bitcoins are legally owned by the customers, not the investment companies. But for most other "investment" companies you're right, although I still think there's still a difference between a state/government holding Bitcoins (where the decision to buy or sell depends on a political decision) or an investment companies (where the decision depends mainly on the decisions on the customers; politics may interfere but it's rather unlikely, at least in "liberal democracies").
OFAC already does that. They have a list of "sanctioned" addresses that they are forcing the American miners to "censor".
The difference to the scenario I described would be that the blacklist could have to be included at protocol level. Perhaps in the same way checkpoints are included now.
Thinking again this may even be possible with a softfork (so no hardfork would be needed), but it's still a fork if there are miners who chose to ignore the restriction and build a chain with the transactions from/to sanctioned addresses.
I'm sure you are aware of the fact that all bitcoins on every single exchange in the world added together is less than 4 million? Buying 5 million bitcoin is impossible, unless you're able to strike deals with holders like microstrategy and buy out ETFs.
This would of course be done over the course of several years and mostly OTC. If the price is high enough, eventually "unconvinced" long term holders (i.e. those who bought "for the money") would be happy to sell. Satoshi could sell them his coins for example

(ok, that's a joke)