I think HA is the system “configure and forget”.
After HA setup and finished configuration, the backup is made.
If no changes has been made later, do I need to backup HA over and over again e.g. weekly?
If you never upgrade or make any changes then you do not need to back up regularly.
However, HA is updated at least once every two weeks… so it’s far from “configure and forget” . Also, I find it hard to imagine that you will get everything “perfect” the first time and you will want to add, delete, change, tweak all the time. Because of that, you should always keep a backup you can revert to in case something goes wrong
So you never want to add new components? Also, I would make a backup after each update to have the breaking changes adjustments.