People holding government bonds is a far cry from a CBDC.

Bonds are large denomination papers that are tradable on open exchanges. A CBDC would be small denomination fungible currency with compability to bank accounts or at least payment terminals at your local supermarket.

It would be really far fetched to transform bonds to a CBDC. There would be so much technological and buraucratic to implement this, this is not feasable.

If there would ever be such a thing as a CBDC in a western country it would begin as a more feature rich tax account with the IRS or equivalent and work its way into the mainstream from there. But def. not from your brokerage account.