I'm feeling a bit silly for asking this, but here goes nothing:

https://imgur.com/a/IMQ3RK7

I've been updating my configs with the fork that someone has created for wadsmoosh to be compatible with Sigil 2 so I can try a run of the whole series through my custom "mod salad" config, and have found that there's no switch to open the gate to the center zone in E1M1.

I've been running some tests, and, while I have a shitton of mods installed, it looks like the issue comes from the doom.wad itself, as running the same installation without the mods (nor the wadsmoosh pk3) also produces this result.

As far as I remember (My installation had a few years already), the doom.wad I'm using is from the GoG's Doom/Final Doom pre-bethesda re-release, and I have never, ever, had any issue of this kind. This said, there's a chance that the wad I'm using actually is from the bethesda re-release, as I think I updated some of the wads, but this happened a few months ago, so...