Technology

Not OP but:

Separate the system and home partition, first of all. The strategies are usually different.

Many distros integrate Timeshift out of the box to create system partition snapshots before every update, and to be able to restore them from the boot menu. Using BTRFS for the system partition makes this even better.

This is usually all that people need in regards to the system, but you can also take regular backups (see below) of things like /etc, the list of installed packages and things like that.

For personal files I prefer Borg Backup because it is incremental, does compression, deduplication, encryption, checksums & recovery.

Borg works with repositories, which can be on local disk, on a removable disk, or remote. If remote, they are tunneled over SSH. It can also export/import tarballs for more exotic scenarios like moving snapshots between different repositories or backing up data to optical discs.

You can use Borg from the CLI and there are also UI apps that make it easier. Pika Backup is a simpler one, Vorta is a more advanced one. I've set up family members with Pika and after preparing it for them all they have to do is plug in the backup HDD, open Pika, and hit the big "backup now" button.

There are also online services that support Borg repositories specifically, and for anything that doesn't you can export tarballs and back them up as regular files, completely transparently from the service.

rclone is a cli tool that supports a large number of online storage services. You can use it with borg snapshots or you can use it to back up your files directly — it resembles rsync somewhat and can also do encryption iirc.