Delirium events in maps?

I did not play the delirium league, so new to the delirium events. I am playing in Harvest and I encountered delirium events during the storyline line zones, but once I got to maps, I have had no delirium events spawn.

I have probably run around 100 maps, so i doubt it is just a fluke. Is there something I need to unlock or an NPC I need to add to my hideout?

as luck would have it, the very next map i did after posting this had a delirium event. I was doing mostly tier 1-4 maps trying to complete all those and recently moved to next tier maps. Perhaps delirium events don't spawn in those starter maps?

Not at all, Delirium can spawn in any maps, be it T1 or a T16 Guardian.

The fact you are not "feeling" it spawns so often is because it was implemented in core in a different way than usual.

Everything that went core before has a 10% fixed chance to spawn in maps. This includes:
> Breach
> Abyss
> Blight
> Legion
> Metamorph

There is the same chance you will stumble in a Breach in a T1 just like a T16. The T16 Breach, being a red-tier map, would just have a higher chance to spawn Chayula (if that rule still applies nowadays).
Addictionally, those spawns do not cancel each other, and multiple league content can spawn in the same map - you can have a Breach AND a Blight encounter in the same map.

Delirium, however, has a 5% chance to spawn. This chance is slightly increased in maps the more Masters, Leagues and other Atlas mechanics are in there.
The official statement is:

"

In other words, if your goal is to encounter Mirrors of Delirium then you are encouraged to use your Zana modifiers, master missions, sextants, and whatever else you have available to you!

In other words, Delirium has more chance to spawn in full-juiced maps, where its laggy fog and its deadly spawns can mow your arse more easily. No tier attached (except, maybe, for the chance of a Kozis' spawn)