How can government "seize" bitcoins? Last year the U.S. Department of Justice posted this press release claiming U.S. &quot;law enforcement seized several thousand Bitcoins on November 3, 2020.&quot;
How is it possible for anyone to &quot;seize&quot; BTC?
My understanding is that it is technically impossible to transfer BTC without the private key for the wallet holding BTC.  And likewise that anyone with the private key can transfer the BTC if they can transmit the transaction.  I.e., short of coercing whoever has the private key to disclose it, is it true that no amount of force or authority can cause or prevent the transfer of any particular BTC?
Or am I missing something?
It is not necessarily true that no amount of force or authority can cause or prevent any transfer of Bitcoin. The protocol does not allow arbitrary seizures or blocking, but there are still human factors involved.
Bitcoin is decentralized, so there is no central authority that governments can go to (or coerce) to force or disallow transactions. However Bitcoin is still owned by people, and people can be forced to perform certain actions that they do not necessarily want to do. While a government cannot command the Bitcoin network to make a transaction to happen, they can go to a particular individual who owns Bitcoin and coerce them to make a transaction
Furthermore, governments often have the power to arbitrarily seize assets owned by people. They can do this by force and physically taking things away. This is often how Bitcoin is seized - the hardware that contains the private keys is physically taken by the government. Once they have access to the private keys, the government can perform any transactions that they wish. There is nothing that Bitcoin can do to prevent this; it is up to the individual to ensure the security of their private keys.

For disallowing transactions, this is much harder. However, as before, there is still a human factor involved. In this case, it's miners who produce blocks. A government could mandate that miners operating in their jurisdiction are not allowed to create blocks containing certain transactions. If all miners were to follow such mandates, then a transaction could remain unconfirmed indefinitely and thus be effectively disallowed.
However this is much harder to do. The decentralized nature of mining means that miners who are in other jurisdictions that do not require censoring certain transactions can mine those transactions. Furthermore, miners who can protect their anonymity and are willing to break some laws can mine those censored transactions too.
Even if no current miner is willing to mine a censored transaction because their governments threaten them, more people could simply begin to mine who do not necessarily follow the same censorship requirements. Mining being decentralized allows anyone to be a miner, albeit at a high initial cost currently. Governments could also try to snuff out the non-censoring miners through force, possibly through seizure or destruction of mining hardware. But even so, people will still be able to mine, and there will inevitably be some miner out there who is willing to make a block that includes a transaction censored by every other miner. So in the end, it really is not possible to disallow a transaction.