If you are getting 500 error while trying to update supervisor and HA here is how i fixed mine.
I am running HA on Proxmox server.
Go to supervisor then System than under Host System next to Ip address click Change change than expend IPV4 and change IP DHCP to static and under DNS server add google DNS : 8.8.8.8 Reboot HA and then update supervisor than update Home Assistant to version 2020.12.1