Upgrading HT-TM05 to 21.02.0

Has anyone had any success upgrading an HT-TM05 to the latest 21.02 version? 19 is running ok, but when I try to upgrade I always get:

The uploaded image file does not contain a supported format. Make sure that you choose the generic image format for your platform.

The checksums check out, not sure what else to do.