Everyone was laughing on Ray Diallo when he said his famous phrase "cash is trash" on 2019 and they even laughed more when his hedge fund tanked 30% under water on early 2020. guess what, US stock markets are bullish again and on a stunning V-shaped recovery and Gold recently hit all time high and bitcoin of course in its way to break new price record. So, who's laughing now!. he was damn right.
Cash in normal states will never be rubbish. Therefore, this expression is generally incorrect. You can call the bolivar rubbish in Venezuela, when constant high inflation has practically devalued it. However, it never occurs to anyone to call the pound sterling rubbish.
Now there is a tendency to digitize the common currencies of states, but this process will be gradual and is unlikely to end with the complete displacement of paper money.