I'm somewhat new here, and I'm just trying to create conversion and learn, so mind me if I come off as ignorant.

Anyhow, I think folding here is fine, really you're only beating sets. JT here is plausible, and TT. But what seems weird to me is why he would bet so much on the river. Like what does he think you have? What hands do you pay him off here with if here does have JT, TT? Hardly any right, especially the way you played the hand. It seems like a very polarized bet and thinking about it a little more he could have air- or close to it.

Make a crazy turn fold or call river. Villain has enough weaker values "monsters" like sets he can easily play the same way. I doubt he ever bluffs, but you beat enough value here,

Eeewww tough spot.
Could find a lot of reasons to call:
-Nits should only have 4 combos max of jt here
-Hearts missed
Nits shouldn't have t6 here at all and we have a 6
-We are so high up in our range that if we fold here we only ever call with jt

However the river bet is huuuuge and unless he is a bad reg he is only betting straights and bluffs with this sizing.
Nits tend to give up when they brick, not fire 100bb barrel and population at 25nl just doesn't bluff these spots enough.

Theoretically a call is fine but I think an exploitive fold is the move here vs this player pool.

What was villains rfi in Co and river aggression stats if you have a decent sample?

RFI CO - 18%. No decent sample on the river aggression factor.
However, i gave the hand some more thought and i arrived at the conclusion that i misplayed turn. With the added equity of my own FD, i feel like i should be shoving turn here facing such a huge bet just to punish villain's 99, because in his eyes i still have some sets in my range that he is happily willing to get it in against.
Might be wrong tho, them 25nlz nits man, never showing you less than the turbo nuts.

This is actually a weird spot, but I see 3 possible lines here: a) Shove turn b) Fold turn or c) Call turn, call river.

The issue here is that people are calling this guy a huge nit, but also saying that this crazy nit flat called a check raise on the flop with a naked gut shot and overs. He's really only comfortable with an 8 or MAYBE a J, and even with the J he's behind our raising range a lot.

OTR he could have 98, 87, TT, sets, maybe JT, but he could also be chopping with us. Some of these hands may check back for showdown value. If we think he only does this with JT then 2:1 on the turn isn't good enough for us to call. But that also means we should shove turn. If he never bluffs river then calling just allows his weaker value bets to realize equity. Either he folds his turn bluff that he was never going to barrel, calls it off with the only better hand, or potentially calls it off with a strong hand because we can have bluffs in our range. Otherwise I think we have to call it off.

The issue here is that people are calling this guy a huge nit, but also saying that this crazy nit flat called a check raise on the flop with a naked gut shot and overs.

That's the main point. How can a nit call a check-raise OTF with JT on a 974r flop? Once he calls OTF and raises OTT, he almost always has a set (I don't think an overpair would be played in this way) so I would shove turn, cause too many of rivers (T, J, 6, 5, any heart) can freeze the action, and for him would be really difficult (close to impossible) to find an herofold, specially when he has 77 or 99.