u/MrChainsawHog

First, what are Yuji's soul attacks?

Yuji's has the ability to recognise the soul, due to inhabiting the same body as Sukuna. This means he can knows the contour of his and others souls. This allows him to "attack" the opponents soul

HOWEVER, In JJK, the soul and the body are intertwined most of the time, so this isn't particularly relevant. However, it is relevant when there are techniques or abilities.

Against Mahito: Mahito's technique treats the soul as predating the body, so when Mahito changes his or other's souls, it changes the body. Yuji negates this by attacking the soul too, meaning Mahito can't avoid damage.

Against Sukuna: Sukuna is a reincarnated sorcerer. You need a form of IT to mix souls, meaning that without it there is always some sort of barrier between two souls. Yuji is able to target this barrier and separate the two souls. This barrier can't be healed because it's not an actual physical thing, it's just the "distance" between souls, hence why Sukuna can't heal Yuji's soul hax

WHAT YUJI'S HAX ISN'T:
Yuji cannot negate durability or change the shape of the soul.

The ability to negate durability comes treating the soul separately to the body, similar to how IT functions.

Yuji does not have this.

If Yuji could negate durability, he would do that. Literally just cut off all of Sukuna's limbs, then spam soul seizing punches until Megumi is free. There is no reason not to use durability negation other than the fact he doesn't have it

Does that clear everything up? Good

Now;

So, now for Yuji vs Denji, soul attacks are...
Straight up a non-factor.

Devils are concepts, they don't necessarily have souls. Soul hax in JJK very well just might not work on them at all, since they're conceptual embodiments
Hybrids can't be separated by any means other than breaking the contract. We literally see not even conceptual erasure works on them, as hybrids were not able to be erased by Pochita. We also see that Makima can't directly control Denji to forcibly separate him from Pochita.
The only devil that was able to "separate" Denji and Pochita was aging devil, whos power negates devil hax...but that didn't even work, Pochita and Denji were still connected, it just let Denji operate independently of Pochita. AND THIS IS WHEN THE CONTRACT WAS BROKEN ANYWAY
If the guy who can literally negate all forms of devil hax, in a verse where devils can create stuff like infinite spaces (eternity devil) can't negate Denji/Pochita's connection, EVEN WHEN IT SHOULD BE AT ITS WEAKEST, I don't think Yuji can.
Even if it could work, Yuji needs a lot of hits to separate souls. It's not an easy thing, even after like 8 black flashes, tens of hits, and 2 Jacob ladders against Sukuna, it only worked in the end because Megumi allowed himself to be separated. The sukuna fight went on for like 30 minutes or something like that, and they were only able to separate a guy who wanted to be separated by the end.
How's he going too survive fighting Pochita and Denji long enough to separate them, especially when neither of them want to be separated?
EVEN IF IT COULD WORK: That literally just summons Pochita, who then just kills Yuji anyway. Even if Denji dies...Pochita can just re-fuse with him, because we already saw Pochita revive Denji, so it doesn't matter all

TL;DR: It is irrelevant

Curious to hear your opinion since World Cutting slash is one of the most Over powered attacks in Boruto Modulo!