How do I get a functional version from before construction broke everything?

[MBurneracc]

I've been running my installs through Stability Matrix which until now worked perfectly fine because Forge wasn't a broken mess. I accidentally updated and now everything is fucked, core features are broken, extensions are broken and all the other crap listed in these many many issue reports.

Stability Matrix handled the installations for me so I have no clue how I'm supposed to find and install a working version otherwise.