Apparently some people are getting corrupted downloads of Linux Mint Cinnamon 64-bit v21.1 from the Internode (Australia) server. Others, including me, are not. The reasons are unknown. I would not jump to any conclusions about the root cause of the Internode download issues.
I downloaded the Shoddy ISO to Cinnamon 20.3...ran the checksum and got OK...so I installed it and look what happened.