replacing a database with pg_restore
Evidently, "root" is not a superuser (which is a bit odd, given the normal implications of the word "root").  The pg_restore command you wish to run must be run as a superuser.  Only a superuser can drop someone else's database, and then create a new database owned by someone else.

Although it looks like the restored database is going to be owned by "root", not "u".  I guess that is not what you are expecting, but it is what was encoded in the pg_dump output.