We used to have gold certificates. If you had a $20 gold certificate and converted it to gold in the 1930s, you would get one ounce of gold worth nearly $3k today.

Then the government did an exit scam, passing a law that the gold trade in statements on the certificates are void. You can still spend one of these bills today though. For $20.

Why should anyone expect any government to indefinitely honor gold certificates?

The only currency that can avoid being devalued by a single government, is a currency no single government can control.