This is a great reminder post.🎶
Although I do love immutable, and use this for my customers as well, I do wonder why at home 2 external USB drives aren't enough in your opinion. I mean, connect them only when creating the backup. And rotate both for each next backup. The rotation isn't doing a lot, just that whenever a new backup is created and something happens right at that time, the other USB drive is there that has the last backup.
To set up an immutable backup at home, seems a bit overdone, though immutable is indeed great. Well, when I can buy this for not too much money, I will go for something like that.
Currently, I don't do this rotation, and perhaps I back up with a little too low frequency. I shall up my game here 🙃