first of all many thanks for your answer. I followed all steps and changed all tables with a little script to the values you indicated. Anyway even if I change it manually in MySQL Workbench it shows utf8mb4_0900_ai_ci as Collation. is this correct?

But finally the result is still the same. It produces these strange binary blobs and running the restore script in order to import it in my local mysql server it gives this result:

ERROR at line 48: ASCII '\0' appeared in the statement, but this is not allowed unless option --binary-mode is enabled and mysql is run in non-interactive mode. Set --binary-mode to 1 if ASCII '\0' is expected.

Do you have any other tipp to solve this?

Greetings