It seems that the Portal Migration process has faced some update from Microsoft, and not a good one.
Migrate portal configuration - Power Apps | Microsoft Learn
The process doesn't work any longer.
After deleting the Website record in the Model Driven App, the same has to be done to delete the Portal, when that is done, an error appears: Something wrong has happened.

Then, when creating a new Portal a message says, something wrong has happened:
No more details than this.
Does someone have any clue about this? Thanks.