Always back up to the cloud in addition to local and external Time Machine backups. Cloud backup raises security concerns, though. This is the best way I’ve found to back up files to the cloud:

Rclone provides end-to-end encrypted backup on many cloud providers. It’s pretty awesome.

Restic is a backup engine which does a few things really well:

1. Creates chunks of consistent size. Cloud storage doesn’t like lots of tiny files, so this combines them together. Also helps split large files.
2. Creates verifiable snapshots with each backup.

This provides two layers of encryption, stored on a cheap remote cloud storage backup.

Steps:

1. Install Rclone and set up a remote to your cloud provider: https://rclone.org/install/ 
2. Set up an rclone crypt on top of that remote: https://rclone.org/crypt/ 
3. Install Restic and set up Rclone as a backend: https://restic.net/blog/2018-04-01/rclone-backend/