I have a question that autovacuum is running on sys tables like pg_class, pg_attribute, is it a normal thing? Further, what is dead tuples are not removed from Autovacuum, can we remove the dead tuples using FULL VACUUMM or pg_repack on sys tables?
pg_repack cannot run on system tables, it will FAIL with an explicit error message explaining the limitation.
Each time you perform DDL operations (CREATE, DROP, ALTER), rows are inserted/updated or deleted into the system tables : pg_class, pg_attribute ...
Autovacuum operations perform "low-level" operations, it can be interesting to perform "middle-level" vacuum with VACUUM ANALYZE... that is not blocking, but will be more a resource-consuming operation than autovacuum.
Performing VACUUM FULL operation will block access to these pillar tables of your database.
If your application/users can handle it, go ahead!
At work on this kind of operation, I set a statement_timeout, in order to properly stop the process if it is over a defined amount of time.