Can someone clarify how the government could launch their currency on the blockchain in the future? will it be decentralized, considering the centralized blockchains are more vulnerable to attacks?

Or they will simply launch tokens on established blockchains like Ethereum, NEM, etc... example: Petro from Venezuela which is a token on NEM blockchain.

Or it could simply be a sidechain to most secure network "Bitcoin"?

Tokens and side chains are not necessarily un-confiscatable.
Would like to hear your thoughts on that matter.