Here are some basics on how to secure /e/ and every OS :
- Encrypt your phone (if not, anybody will be able to access everything)
- Set a good password (to prevent brut force)
- Apply the updates (which bring security updates)
- Do not install unknown or weird or untrustworthy apps
- Do not root your phone
- Limit authorizations asked by apps to the bare minimum in Security & Privacy > Trust (ou Protection des donnés en français ou quelque chose de similaire), then long press on any app you want to configure deeply
- Do not let your phone without surveillance, someone could install something bad through TWRP but it’s very unlikely.
If you respect everything, you won’t face any issue (or you are the less lucky person on the internet).