Web - what is the differences between periodic sync and sync?

I came across two different types of sync in the background for PWAs sync and periodic sync. there are not many resources for them and existing resources do not explain enough with sample working codes.

so my main question is: are there any other logical differences between them other than frequency?

and my side question is: are they handling requests by themselves? I'm asking this because I want something more flexible, I mean I'm managing offline and online situations and saving data in IDB them I'm offline and I just need a background process to get my offline data from my custom IDB and send them to the server.