You can tick off this task if you simply don't use a feature phone.
In the event of confiscation or raids, contacts, text messages and call lists can be read. What's more, dumbphones are just as vulnerable to mobile network attacks without additional protection. Dumbphones cannot be encrypted, you cannot install apps such as password managers on them, you cannot clean your pictures of metadata and you cannot use secure messengers.
Civil society actors or NGOs often work with vulnerable groups. A feature phone, for example, is not able to encrypt and adequately protect phone calls or text messages.
On the one hand, these phones have disadvantages. On the other hand, it should also be noted that non-smart devices completely eliminate some dangers. For example, the risk of infection with malware is much lower here. However, encryption and secure communication seem so important in the face of inflationary confiscation and surveillance that a smart device is often preferable.
This tip is by no means intended as a statement against digital detox. If you feel that a feature phone supports you in this, that's OK. But now you know the potential dangers.