ODroid C2 cannot update to 6.12

Please help! When trying to upgrade it from 6.11, it fails at getting Jessie Security. Either the file format is incorrect or the file does not exist.

Jep, for some reason arm64 support on Debian Jessie security repo was dropped. We fix this with v6.12 but the issue prevents the update…
You need too manually remove the security repo: https://github.com/Fourdee/DietPi/issues/1915#issuecomment-405341067