The problem with all these is that money is kinda worthless if you're unable to spend it, and regimes that are likely to enact such monetary policies will often regulate the use of gold etc as well. A bunker full of gold bars does you no good if actually trying to spend any of it is a crime in and of itself.
I agree, and when I see foreign currency as an option I think of two possibilities. First, moving to the country that hosts that currency. Second, waiting for the US currency to slide into obscurity and switching to whatever takes over as the global currency.
Both are tough choices that rely on either too much time or too much space.
It's not a fantasy scenario that we need to speculate about. Currencies collapse all the time, just pick any country and it has happened to them within the past 200 or even 100 years. There's millions of people alive right now who avoided having their life savings destroyed by having foreign currency or bullion or both.
I'm not disagreeing with that part; I grew up in Russia in the 90s, where, if you had any significant amount of money, you'd have a dollar or euro account, and ideally both. This provides security against currency collapse, yes; but if the government decides to be actively confiscatory, it doesn't really help, unless their plan is particularly poorly designed.
If we're talking about physical paper money bills, then the government will not be able to confiscate these from people, they can't search every nook and cranny for something which is so easy to hide. The way the Finnish government confiscated money was by imposing rules on how their currency could be used and the value of the bills. For foreign currency, they can try to impose rules and a fake exchange rate, but the rest of the world is not going to care, neither will the black market.
If we're talking about digital foreign currency, it's a matter of having that money in a foreign bank account, where your government can't touch it. Everybody should have some or most of their money in foreign bank accounts, otherwise you're practically begging your government to ruin you.
By "confiscatory" I mean any policies that amount to taking your money or preventing you from using it as money. With physical paper money bills, making them outright illegal to hold is actually surprisingly effective - you don't need 100% enforcement rates, just high enough to make it impractical for most people. One historical example of such a society was the USSR.
I didn't know we were talking about "most people". They will do whatever their government tells them to do: hand over any property the government demands, and send their children to the trenches to die.
If you want a solution for most people, the solution is to not have a communist government or any other government that will confiscate your wealth.
If you want a solution for yourself, it is bullion and/or foreign currency. If the government declares their own currency as being illegal to hold, then that currency now has a value of 0. For you and for everybody else. If they declare foreign currency as being illegal to hold, that only has implications within the country. And the black market does not care about borders.
If most people won't take your dollars/gold/... because they fear getting caught, then what use is it to you? You won't be able to spend it. There were actually people like that in early Soviet days, guys who managed to preserve a stash of their former wealth, but without the ability to use it meaningfully.
The best mitigation you have for that kind of government is having a ticket out.