Which component of Mule 4.1 replaces Mule 3.9 <timer-interceptor> ?
None. Mule 3 interceptors are not supported in Mule 4. You might rbe able to replace them somewhat with custom policies, as mentioned in the migration documentationhttps://docs.mulesoft.com/mule-runtime/4.1/migration-core
The reason is that Mule 4 architecture is very different in thread management and it doesn't allow the interceptors implementation.