I can ping google OK, but I get a "Destination host unreachable" for GitHub, so that is probably the cause of the error. I tried a few other sites and they gave the same error, so it looks like for some reason I can only access Google, although the Pi-Hole does work ok.
Okay, that's something you'll have to fix on your network, it's not a Pi-hole issue. The packets aren't getting past the first hop and if this is on your local network, that would be the router.
If it was DNS then you wouldn't be getting the public IP address of GitHub as a query answer.
Looking again at the debug log, it looks like pings from the Pi-hole to the router are failing. So there is something on your local network that is not configured correctly. Since the cause of that could be a wide number of things that all are unrelated to Pi-hole you will have to troubleshoot the connectivity yourself.
Your setup also needs some adjustment. The IPv4 address matches the network check on the Pi-hole node. But it seems unable to ping 192.168.1.1, the IP you have set up as the router for your Pi-hole and DHCP clients. The IPv6 address does not match any IP address assigned to the Pi-hole node so check that to see what the proper IPv6 address is. (Compare to ip -4 addr list and ip -6 addr list to see what IPs are assigned to your Pi-hole nodes interfaces.)
I managed to resolve this in the end, I had a very stupid mistake in my network configuration that I'm embarrassed to mention. Once I fixed that I was able to update ok.