1. There is no question about Fiat money (whatever it is $, £ or euro.) thats its losing it's value, so the question is. If it got no value what value Bitcoin have then ? ( i will use bitcoin for must common crypto but thinking of any). Can't get my head over it.
The easiest answer here is that fiat will never lose its value.
It is true that the value of each fiat to others is changing but you should always remember that fiat is centralized. It is controlled by the government in each country and they find ways to retain its value even though they are printing a lot of it. Bitcoin's value will be the same, it is just that Bitcoin is not that much used and people commonly used fiat that is why they are converted into it.
2.If you imagine in let's say 20 years FIAT goes to CRYPTO all the way. You want to buy a car worth $5000 but paying in Crypto, how much would you pay ? if $ got no value.
Then how will we price it if $ has no value and its price is $5000, right?
Obviously we would be paying cryptocurrency in its own value. If the main currency of each country, let's say is Bitcoin, then obviously they will price that car into Bitcoin for example one Ford Everest costs 5 BTC, then I would pay 5 BTC nothing more. You don't need to add something without value since it has no value.