How to create a project where all data will be encrypted?

Interested in how to create a project correctly, where all user data will be encrypted? For example, how to make AES-256 encryption for private messages on a regular forum? Also interested in how to make data encryption for any CMS? For example, I have an engine where all text data is stored in a database, I need it to be impossible to decrypt, also in this engine files are stored on the server in open form, it is necessary that they are stored in crypto-containers that it is impossible to open without the decryption key. How difficult or easy is it to take a ready-made engine and do data encryption, or how best to make everything well written and properly arranged? Maybe someone knows CMS where there is already encryption AES-256?