When the US went off the gold standard, dollars had no real value other than the fact that people just believe they have value. It allows the government to print as many dollars as they want and because people just assume they have value, it didn't have any adverse effects.
Crypto works the same but with a much more limited amount of supply. It's scarcity that creates value. Gold doesn't really have value ... there are some industrial uses for gold but this doesn't explain why humans value it so much. What's the difference between a gold necklace and a plastic one? They are both necklaces except gold is rare, so it has more value. If plastic were more rare than gold, it would have a lot more value.