Plesk migrator -post migration

Hello,
I have recently performed a migration using Plesk Migrator. Now all data is transferred from the old server (Ubuntu 10.04) to the new server (Ubuntu 20.04). How can I test if all functionalities are working? The preview function in Plesk is not helpful, because there I am redirected to the old server or get a 500 Error. However, I do not want to change the DNS entry until I know that all functionalities are working.

Greetings,
Jan