I tried it with ARMv8, but it was the exact same, so I went back to v6.
I think I may have narrowed down the problem. I found this post, and I ran the code on there: https://dietpi.com/forum/t/cant-update-dietpi-failed-to-fetch/5272/1
I’m pretty sure this is a registry problem, as DietPi is trying to download files from port 80 here (http://93.93.128.193/) yet those aren’t there. I ran the code from the other topic, and it seemed to work; it found quite a few of the files that were previously missing, but many it couldn’t fetch.