Edit: An issue with the wrong install file referenced in the install instructions was addressed in the meantime.
Before
The linked guide says “Have the OTA zip linked downloaded”, but …
… the files there are not OTA ZIP files and can not be ADB sideloaded (they are for installing with fastboot according to their content as well as the Murena One command line install guide).
For Murena One users on stable (how to check), the OTA ZIP file is available here … https://ota.ecloud.global/api/v1/one/stable/ (note the missing “IMG-” in the filenames).