Alpha-numeric characters up to 20 bytes in length. If you enter a value that is longer than 20 bytes, then the system truncates it to the first 20 bytes.Reference - https://experienceleague.adobe.com/docs/analytics/implementation/vars/page-vars/events/event-serialization.html?lang=en

Hey Folks - Just following up on this. Is there a way to increase character limit of serialized event Id?