Grant privileges to tables in all (dynamic) schemas
Just omit the IN SCHEMA clause, and it applies to all schemas, so no wildcard capability for schemas is needed.

ALTER DEFAULT PRIVILEGES FOR ROLE my_role GRANT SELECT ON TABLES TO my_role;


Your real problem is likely to be the FOR ROLE clause.  The above is kind of useless, as it applies only to tables (in any schema) created by my_role.  But the creator of tables automatically has select privileges, so this doesn't do anything useful.  Your FOR ROLE clause needs to specify who will be creating the tables (if you omit it, it means the current user).  If you have multiple such creating roles, you have little option but to repeat the ALTER DEFAULT PRIVILEGES for each one.  This is where the wildcard capability is really needed, but sadly does not exist.