Counterfeiting is a serious concern. The fact that dollars and other currencies are counterfeited does not change the facts about crypto: That its volatility and total lack of consumer protection render it useless as a legitimate medium of exchange. Kind of like a man being brought to court for murder and saying "Well what about so-and-so who smokes pot?"
Governments have law enforcement arms dedicated to stopping counterfeits of their currencies from hitting the streets. The US Secret Service was created for that job, protecting government officials came later. They also are tasked with protecting from cyber-based crimes. I have heard they are the most effective law enforcement agency in the US government, though I can't find the cite at the moment. Domestically they intercept over 99% of all counterfeit currency before it hits the streets.
Physical currency is also a tiny fraction of the total of all things denominated in dollars worldwide. I've seen estimates between $1.2 trillion and $2.1 trillion in physical dollars in circulation, but the total is several orders of magnitude more than that. I remember in the 2008 financial crisis the total losses were around $80 trillion. That's just the losses.
The Wikipedia article
@heltok posted about superdollars only mentions in passing that the $100 dollar bill implemented security measures in 2013 to counter the counterfeiters and I noted that all the examples in the article are from before 2013.
Counterfeiting coins is kind of a niche business because the only coins that would be worth counterfeiting would be ones that employ precious metals and replace the precious metals with base metals, though it would be very difficult to get the weight right in that case. Almost all coins in circulation today are made from base metal and they are likely going to cost a counterfeiter as much or more than the coin is worth. There is a reason counterfeiters focus on larger denomination notes and not $1 and $5 bills.
The counterfeiter of Euro coins is probably the Chinese state itself and it might be for funding intelligence operations in Europe. Nobody is getting rich doing it. Even for a Chinese mint with Chinese labor costs, the cost to make each fake Euro coin is going to be close to the face value of the coin.
All that aside, government issued money also has an enforcement arm to curb counterfeiting and illegal activity with their money. A lot of counterfeits are caught, but obviously the failure of the war on drugs shows the failures to stop illegal activity. However law enforcement exists and they do catch people who are participating in illegal activity with their money.
Crypto currencies have very limited or non-existent enforcement arms. If someone figures out how to hack or manipulate a currency, they could make it worthless in a short time. The US dollar is the world benchmark currency in large part because even though there are bad actors, it's very difficult for one actor to do major damage to the currency and the law enforcement arm behind the currency catches any fish that get big enough to even pose even a minor threat a threat domestically and puts a good dent in bad actors worldwide.
Maybe nobody will ever figure out how to hack the blockchain of crytocurrencies, but they are all one hack away from being worthless.
It's also possible that crypto may survive and become a valid part of the world economy. IMO it's healthy to be cautious about these things.
@heltok said above that the stock for a number of companies like Tesla and Apple followed the same tulip mania pattern. There are a handful of companies whose stock followed that pattern that survived. In each case they had a compelling product and a good brand reputation. The history of the 90s is a tale of flash dot com stocks that came and went because they were big on hype and low on real value. Those all followed the tulip mania pattern too. The EV industry has seen companies come on the scene with a lot of fanfare and only one has made it to profitability with their stock worth much today.
Sometimes a boom is something that will be of major value in the future, but for every thing that booms and does well, there are 99 things that boomed and died. A smart investor who keeps their head can make a lot of money off booms that eventually go bust if they are wise enough to jump out at the right time. But that's playing the herd against itself. Finding the real long term winners in a field full of future losers is tough. Many of those who jumped on the Tesla bandwagon early and did well think it's easy, but in reality you won the lottery.