However: 1. That has no bearing on how much they actually spend, which is what was being discussed and 2. Neom is much more than just The Line. As you can see from the YouTube link I posted, Sindalah seems to be on track to open this year, which is part of Neom.
So while Neom overall might be behind schedule (and The Line or other components may never open), it is clearly not an "imaginary" project given that parts of it will open soon.
If that were the case then Stargate is already a thing because OpenAI must have a data center somewhere already.
And yes, the plan was for it to be 170km, since it was announced.
From there, The Line =/= Neom. That said, 170km is still the plan for The Line – the first segment was supposed to be 5km by 2030, now it is 2.5km by 2030. And again, them not building as much as they said does not mean it is cheaper (cost is what we're discussing, after all). If anything it means they are already over budget.
Stargate is a new company, so OpenAI (a different company) having data centers does not seem relevant. Also, I do not think OpenAI actually does own any data centers – for the most part they've been using Azure infra AFAIK. But I did not claim that Stargate was imaginary, so I am unsure how this is a relevant point for you to make.