The UK has a passive Bitcoin strategy, holding $3.67B with minimal recent transactions.
The UK has not publicly acquired Bitcoin, I might also be wrong. But from reports, most of their Bitcoin acquisitions come from seizures, like the US. An example is about 61,000 BTC confiscated by the UK police in 2018 from two Chinese suspects
Jian Wen and Zhimin Qian. It was suspected that these funds were obtained from investment fraud executed in China.
I wouldn't include the seized assets as a reserve for a nation. The chances of them selling at the market price is way more than the others you mentioned. US Government has never publicly bought Bitcoin or consider it as a currency as compared to El Salvador, just taking an example here. So I don't think you should have two extremes under one list like this.
Seized Bitcoin can easily be sold, as we saw in the case of the federal state of Saxony. The law mandates the Dresden Public Prosecutor General's Office to sell such coins in certain conditions. However, the selling of these seized assets will depend on the politician in power. Trump has promised not to sell any Bitcoin in US custody. Rather, it will be a strategic reserve currency.