Can't pass througth sertain arrousal treshhold.

It could be a lot of things, you might need to try different ideas.

It could be the case that there's some deep mental resistance, where you're not giving yourself permission on some unknown level. Which might be something really obscure. Or you could be trying to steer things, when instead, the time has become right to let the session take on a life of its own. Maybe you're too locked-in to feeling pleasure in one place, or pleasure of a certain kind, whereas the sensations could evolve into something else, maybe something entirely new. Maybe you're feeding the session something it doesn't need anymore, like you've gotten to a stage where it just needs you to be quiet, hug yourself, stop thinking, and feel cozy. Crossing over into a release phase of an orgasm can feel very different than the pleasurable build-up stage, so you can't get tunnel-vision on one kind of sensation, or expect the orgasm to "take" you in the way a traditional orgasm would.

It could also be that you've got some wrong expectations about what the next level looks like, and you're stuck waiting to feel something that isn't coming. Like you might be used to feeling A then B then C, and if you're stuck at A waiting for B, you might just be able to skip straight to C, but it's such an unfamiliar transition that you don't believe it's possible, or can't even imagine how to shift there. Some of my best peaks had me feeling like "This isn't how it's supposed to work, is this even allowed?!".

These are just random suggestions, but there are many weird and unexpected things going on.
Like one phenomenon that keeps coming up for me is a tender lower-belly. When things are going very well in a session, I feel a distinctly new sense of relaxation in the area just above my pubic bone. It's such a deep relaxation that it makes me feel especially vulnerable in that area, like I'm worried someone is going to punch me there, that I'm too off-guard. Is that some weird shit or what?