I found it at last. The footage that one anon recorded. Now I can make the post I wanted.
So in the language files you can sometimes find dev text. It's a fun glimpse to the devs describing scenes, sometimes unused scenes, or whole cut scenarios.
Here it seems like instead of fighting Stranger, you'd have had an alt version of the existing Something fight but in a failure state. Calm Down, Focus, and Presist would fail just like the Stranger and Basil fights. Eventually it would turn into the Blurry phase of the fight, but Sunny wouldn't be able to face the memory any further and the fight would end in failure. As seen in the footage below.
https://files.catbox.moe/s8iiqm.mp4
Then, sort of like the Omori fight, you could choose to retry or give up. And if you retried, you'd start the fight as Omori, according to the dev text you'd unlock Omori's Red Hands skill, and it would play out something like this but presumably more polished if it was final. Also without Dream Aubrey, obviously.
https://files.catbox.moe/igc2l4.mp4
Then things seem like they'd have played out the way they normally do in the final. It's interesting because the time frame for this change seems tight. The 2019 Build had a completely different Black Space ending scenario where you'd find Dream Basil and just guide him out of Black Space by retracing your steps, no Stranger or Something fight. Back before Black Space and Black Space 2 were split. And considering they had both the Something fail fight and Omori defeating Something fight somewhat coded, makes it seem like the Stranger fight was a pretty late change.
I think. The development of Omori is so interesting.