The blog post Evergreen: Serverless Functions & Compute for Customer 360 Platform you link to says:
A limited access developer preview of Evergreen will be available with
the Spring ’20 release in February.
A starting point to get on that (so you can try Evergeen out) may be the sign-up link that immediately follows.
But when/if this feature will ...
In HTML you do not need to loop because you are working with a single event record.
In html write:
<div class="formfield slds-list_horizontal slds-border_bottom">
<div class="formfield slds-border_bottom slds-list_horizontal">
Well it's ugly but it SEEMS to work:
Event e = new Event();
Map<String, Object> untypedEvent = (Map<String, Object>) json.deserializeUntyped(json.serialize(e));
// put other fields such as pattern
e = (Event) json.deserialize(json.serialize(untypedEvent), Event.class);
system.debug(e.IsRecurrence2); // ...