I would assume you can still have physical cash with CBDC. Central bank will just have to guarantee equivalent amount of CBDC when paper cash is presented. Just like they used to do with gold and silver in the past.
But with more and more people having access to mobile phones, governments can easily create wallets to make CBDC easily accessible.
You are right though without authoritarian powers, it would be difficult to implement when there are better alternatives. Question is whether central banks can compete with open networks.
Still, competition is good and hopefully this will lead positive outcomes, instead of banning the alternatives.
That would defeat the purpose of a CBDC the whole point of it is to have it be programmable to add certain incentives and disincentives and to remove the anonymity of money, it would also break the fungibility of your medium of exchange as stores and people would value physical cash at a premium over the CBDC
Programmable money sucks. Money should be fungible. And perfectly traceable money cannot be fungible.