General Question about Securing Private Chat , Video , File Sharing

We are wanting private conversation via chat, voice, video, and document/file sharing

We are looking at an app to do this.

-Anyone using Threema?

-Are there any device or other related concerns that would jeopardize the security that the app is intended to provide ?

For example:

  1. Destop/laptop Settings
  2. Web cams
  3. Microphone setting
  4. Cellular device settings
  5. Alexa, Google Nest, Etc.
  6. VPN Use
  7. Best way to encrypt and share files (maybe using Yubikey or similar)
  8. Pros/Cons Of “Encrypted” Files/Folders on One Drive or similar
  9. Best Way To Secure Apps or Data on Mobile Phones for Android and iOS, ie encrypted and/or secrete folder, etc
  10. Any similar considerations

Does anyone have a white paper for this topic and or could you suggest where we might increase our understanding of the topic.

Thanks.