Also one bit that people tend to forget about Niji 3D debuts is, universally, they had nothing to do with time you spent in the company. It was about the order in which livers reach specific milestones, and unlike Holo (who also have this requirement) you are not guaranteed to do so before you even debut. iirc there are still some og JP members who haven't got theirs. Then instead of a regular stream they are first shown at NijiFes as a small appearance, and only then at some point in the future you might get to have a proper 3D debut. NijiEN supposedly all getting models for AR event must've made a lot of friction between the company and it's existing JP members who, despite reaching required threashold ages ago, still didn't have their debuts. Which probably contributed to initial cancellation (but most likely is the fact that Holo had a big event with like 1-2 weeks difference in time or something). Elira getting 3D "debut" way ahead of everyone else had nothing to do with favoritism in EN specifically, but rather the whole system is rigged in favor of popular members while ignoring unpopular ones
Really late reply (I was going to reply to this but I fell asleep and woke up late), but what you said is correct.
To my knowledge, they have a systems where to get the queue (yes, a queue) for 3D debut you need to reach milestone of 100k subscriber before you got in there, and the assumptions we have is that EN and whatever remains in ex-ID and ex-KR is in the same queue with JP. It basically means that if, say, a EN talent like Vivi/Victoria Brightshield got her 3D model, she would be in a queue with no possible ways to know
when she going to get those 3D models to debut.
You are also correct, in that the talents got their 3D models by appearing in nijifes or concerts before having proper debut. That said, it also depends on the situations on how
long you can actually read to properly debut it. Everyone here knew just how that part happened when Hana's 3D revealed during Nijifest 2022 but her actual debut had to be delayed twice and debuted it properly like, in april on the next year, but there are also talents that have their 3D appeared on nijifes/concert but for some reason or another, has not been able to debut properly, if at all.
That said, I don't think the bit about EN getting 3D models for AR event would be the catalyst of 'frictions' to the point of it getting cancelled with covid excuse, especially considering that apparently the EN talents spent their time going to Japan for it. I will assume that at the end of it, their in-house team is just wasn't able to quickly prep 3D models for the concert and keeping with whatever timetable they have for it. Lazulight getting the 3D done for their nijifest appearances and their debut are probably because it's the ones that they have done and finished (even if Pomu's still bugged out), allowing them to get an early start.
Who knows if there's something behind the scenes that allowed the three to debut it first that we don't know off, but I just gonna imagine it as a pragmatic reason, aka ANYCOLOR taking their best chance of these three currently together in Japan to immediately debut their models before two of them flew back to the hellish landscape that is Canada.