Same boat as you. I used to run LSPDFR a lot and could fix just about anything, but I’m rusty now.
Anyway, I recently came back to it and ran into a similar issue—GTA V updated automatically, and suddenly nothing would launch. I had a ton of stuff packed into my mods/update folder that I didn’t want to lose. I tried bringing all my old modded files back (like common/data, dlclist.xml, etc.), but the game would crash on the loading screen every time. No error, just a hard shutdown.
What I ended up doing:
I copied the full, clean, updated update folder from the game directory into the mods folder to replace the old one.
Then I downloaded and reinstalled most of my previous mods—NaturalVision R, AI behavior mods, gameconfig, visualsettings.dat, etc. I avoided dragging over old files wholesale—almost every one of them was crashing the game, probably due to version mismatch or broken references after the update, I don't know.
The only old file that didn’t break anything was my visualsettings.dat, oddly enough.
So yeah, unfortunately, I couldn’t salvage most of my old setup. Reinstalling fresh was faster than testing a hundred files one by one. It also helped because a lot of older mods are broken now or need updates anyway. Just my take—but I get not wanting to start from scratch; I didn't; I spent two days trying to figure out the broken files one by one before giving up!
P.S. After replacing the update folder in the mods directory, I still had all my old DLC add-on vehicle packs in place. Once the gameconfig and core mods were back in, I could finally edit the dlclist.xml again without crashes. I added back all the lines for my custom police cars/addon DLC pack, and everything loaded fine—got all my old vehicles working again.