The theories come from concerned critics mostly. As far as I know there has been no discussion as to how the government might influence the functionality of a CBDC.
The above has some chatter about non-US nations exploring the expiry/programmability aspects.
Also, nothing stops people from buying the goods in question by using a payment service provider/bank that provides a layer on top of the CDBC and automatically circulates the money for you behind the scenes to avoid the expiry.
Eswar Prasad, WEF Annual Meeting of the New Champions, June 2023