The US holds the largest Bitcoin reserve at $12.16B, mainly from law enforcement seizures.
They are holding on what they did not invest, instead, it's what was taken away as seizures from the illegal achievements from others, such as scam, fraud, hacks and their likes, US should not even be seen as an holder by any chance because they only take advantage on making seizures from their subjects.
The UK has a passive Bitcoin strategy, holding $3.67B with minimal recent transactions.
Fairly, we can talk much of IK than US in terms of holding capacity, at least, UK are still better discussed on this than US.
Bhutan and El Salvador actively manage Bitcoin, with Bhutan also generating income through mining.
Bhutan are mining Bitcoin while in El-Salvador, Bitcoin is made a legal tender, mining takes place as well as many other Bitcoin network activities that encourages for crypto adoption in the country.