Yes, I am using Window10.
The previous error was duplicated when I used the qsys file 20.4 version which was sent the second time by Ben_C through email.
This time I tried to reproduce the same problematic qsys file 20.4 version using the qsys file 20.3 version (sent first time -which does not cause any error initially in Quartus v20.4) by Sync System Info in Platform Designer - the flow that you provided on how to migrate the qsys from 20.3 to 20.4.
The error does not show up at the end, in order word, I can't reproduce the same problematic qsys file 20.4 version by migrating the qsys file 20.3 version from Quartus 20.3 to 20.4. I am trying to debug could this be Quartus setup issue or machine issue. Do you are able to reproduce the problematic qsys file from the good qsys file with a different machine?
Hope to get your understanding.