Soon cash will not exist. Banks and governments around the world have been discussing removing notes/excluding them as legal tender, in order to lock people into the banking system. From here comes chaos. Anyone can be excluded from the economy at the click of a button, and this will probably end in the exponential growth of Bitcoin. I digress from the main point of this topic however...


Your idea is fine however there is a flaw - In order for this idea to work, a central party would need to provide this tender and therefore they would have access to private keys. This would be the equivalent of a custodial wallet.

Or, an open source tool is created to create your tender, which you can then create notes yourself and spend them yourself. The private key being its authenticity. To make this work though, merchants and others who are accepting would need to be able to have a tool that can sweep the private key. The next problem from there, is change. (e.g, I have a 0.01 BTC tender item, though I am buying something worth 0.009 BTC. How do I get the 0.001 BTC change, and what is stopping this amount from being swept by the seller/merchant/receiver too?)

The next issue after that, is the design standard. Since a private key is all that is needed for valid tender, what would this look like? How do people distinguish amounts (as there is nothing stopping all possibilities of design). I suppose Ordinals or NFTs might even be useful here...

Creating an offline option is possible, but not as simple as it seems in theory.

Any digital currency (both fiat and crypto) is vulnerable to network failure. That's one of the main problems with cryptocurrencies: they can't exist in non-digital (material) form. So network stability (at least at the level of core hubs) is vital for the existence of cryptocurrencies.

Not only Bitcoin but today everything relies on internet connection and banking services you are talking about also need it so internet can never go off permanently because it would cost trillion dollars of loss to the whole world if you understand how everything is connected with it.But with btc for some time transactions would not happen but after that everything would be normal like in LN you have to broadcast the main transactions only so in future there could be more possible solutions for it we don't need to worry about it.