Holy shit dude, you really want to play this game don't you? The best advice I could give you is stop, it's not worth killing your computer! I know some people had performance issues but I've not heard of anyone having it close to this bad, which is probably a bad sign for you. Do regular games with similar requirements work? I would suggest you check you're on the latest version, but it really doesn't sound like that'll fix your problem.
You could say I enjoy this game,I wouldnt say fell in love, but I reallyed enjoyed the first one and so seeing a second one alittle more flushed out is making me all sorts of jumpy and happy.
As to answer your question for parts, ive played a multiude of other games, Red Dead 2, DS 1,2,3. Baldur's Gate 3, FF14,Monster Hunter World, Spell force 3.
Like I playsome pretty hard spec requirment games, but my pc is REALLY good.
Ive only ever had this problem ONCE before, with a trilogy game that was ported to PC called .hack//G.U. Recoded. which was amazing to play and I had so much fun, but I couldnt get past the 3rd game of the trilogy, the final boss would do something very similar to me at its final stage, the frames would drop down to none exsistant and just in general my pc became slow till it went *Poof*
Although with that particular game, I just as a final Hail mary after like the 8th time trying to figure it out, just lowered the graphics to none exsistant (Which really didnt alter ANYTHING visual wise or performance that I noticed) and I could do that fight, and even stage three went smoothly, which was jarring since. you know. seeing thatfight in slo-mo for 8 times in a row, andthen its suddenly fast, I died to say the least since I wasnt used to the new speed I had. but back on topic.
Nothing Fixes this issue, and I over qualify for the game specs, I dont know what causes it, and I have no idea how to fix it, to say the least its beyond the point of "This is mildly upsetting" this is "I am bored now because the one game I wanna play and paid good money for, I cant play."
I should also add that these problems, only seemed to happen after I installed the R18 after finding out that it wasnt R18 Default on Steam... so maybe it was the file I downloaded for the R18 fucking with everything?