I will do that.
But I also note that Pi-hole v4 worked fine when I installed it on a fresh Diet-Pi today. It was only after upgrading to v5 that the saving issue appeared. I'm assuming there's something different about how the web server user attempts to write to a database in v5 vs how it wrote to local files in the /etc/pihole directory in v4 and that's what's causing the error to appear.
I suspect that once v5 is out of Beta, the Diet-Pi devs will incorporate it into their software installer. I suppose it's also completely possible that this issue goes away when v5 is able to be installed fresh.