Looking at the after-install.sh file from the x86_64 version, it sets up some policy files and security groups and makes a few symlinks, then attempts to register the package sources for your distribution. But based on the above conversation, it looks like the packages are not yet available for aarch64.

So, I just copied the after-install.sh file from the x86_64 version and edited the script to comment out the code that installs the package sources (the call to installAutoupdateChannel at the very end of the file):

```
installFiles

installAutoupdateChannel

exit 0
```
Running that script appears to have done the trick on my aarch64 RPi 4