That is true, no investment plan is 100% safe, but out of all cryptocurrencies, investing in bitcoin is safer than others, this is the coin I can tell people to invest and hold for long.

That your link is simply about DeFi and yield farming in a way people can invest to make the coin they buy to take part in a pool of making transactions fast and in the process, it will earn an active income. This can be good for stable coins like dai in a way you still earn money when you stake stable coin.

But on the other hand, there are some altcoins you will stake, earn more coins, but the value of the coin your staked and that you earned with not worth the value of fiat you initially used to buy and stake the coin because of price downturn of the coin you staked. It is still very good to be careful of the coin you want to stake.