どうも設定場所が変わったようです。
Encrypt New Data in Standard Fields
Depending on the size of your org, enabling a standard field for encryption can take a few minutes.
- Make sure that your org has an active encryption key. If you’re not sure, check with your administrator.
- From Setup, in the Quick Find box, enter Encryption Settings, and then select Encryption Settings.
- In the Advanced Encryption Settings section, click Select Fields.
- Click Edit.
- Select the fields that you want to encrypt.
All new data entered in this field is encrypted. By default, data is encrypted using a probabilistic encryption scheme. To apply deterministic encryption to your data, select Deterministic from the Encryption Scheme list. For more information, see “How Deterministic Encryption Supports Filtering” in Salesforce Help. - Save your work.
https://help.salesforce.com/s/articleView?id=sf.security_pe_enable_standard_fields.htm&type=5