Hi Ihab,
Not sure where you read the requirements. The requirements I am referring to is from here Create an ArcGIS Enterprise backup—Portal for ArcGIS | Documentation for ArcGIS Enterprise
If you are talking about the portal admin account, you don't need to have the same username and password across source and target, because you can still change username and password when you restore your backup in the target environment. Just make sure you edit the "webgisdr.properties" in the target before you run "webgisdr --import".
If you are talking about the Service account, the requirement is "The domain account or accounts you use to run your ArcGIS Server, Portal for ArcGIS, and ArcGIS Data Store services must have write access to the shared directory you specify for the backup files." In other words, this is about the permission, but not password. You may have different service account such as "arcgis" in your source and target, then you need to ensure your source "arcgis" account have read/write access to all the relevant directories in your source, and target "arcgis" account have read/write access to all the relevant directories in your target.
Hope it makes sense.
Cheers,
AB