Oooooh, glad you're doing this.
Naturally, I'm in.
I'd give you an opinion if it weren't for my severely sleep deprived brain yanking any desire to actually think away from me but I'll keep you in mind next time we'll talk.
OPINION:
MBIT - INTP
ENNEAGRAM TRITYPE - 3w4 5w6 gut type ? It could relate to either 8w9 or 1w9 and I'll explain although you do not relate much to 9 in the thing below here.
I feel like INTP fits better for you. ENTPs and INTPs can look a bit similar but INTPs are a bit more in themselves. Basically the idea here is that you are dominant Ti, and your Ne is used to find patterns and data to back the focus of the Ti, which is always wondering how things work. The Si allows a mini storage of this knowledge, which help organize the TiNe findings for a later date, but also gives you an air that may come off arrogant to some because it is more calloused and objective. Sometimes introverted types mistake their dominant function for the one they extravert. Since Ne is the first extraverted function, often in interaction you'll use it. It helps you make those silly jokes you make.

Last is Fe, which blends back to wanting to use your knowledge for a greater objective purpose. But you may not realize you even use the function much, since the ethics function can be a real blindspot for some INTPs. The biggest flaw an INTP may have with their emotions is rather than letting them be they may instead try to bring logic to them, and since emotions aren't really logical, they pick apart their own feelings to death.
As to enneagram, I see no reason why you can't be a dominant E3 and INTP. I always notice E3s have this style of thought and communication that...stands out to me. that usually I struggle with. I think you adapt pretty well for an E3 though. 3w4 I think is fitting more because I haven't seen an ounce of E2 coming from you. XD 5w6 seems accurate and I have no arguments with it either. We were discussing headtype for you and I'm gonna bring up how maybe you can decipher if you are E8 or E1, because I don't think you are E8.
First hand, you discussed control. Gut types are confusing because with gut types, it isn't totally about control. It appears to be about it, but I have found I understood gut types and where I was when I understood where the anger points to. Every gut type has a different spot that angers them. If you mess with the idealism of the 1, the 1 bites you. If you mess with the independence and freedom of the 8, the 8 bites you. If you mess with the merging and way E9 is seen socially, they bite you. E9 is conflict avoidant but I've found calling out an E9 in public is a great way to make an E9 fight you. I wasn't trying to get them to bite me, but I've found they definitely don't like it. XD
I do think you have assertiveness to you, but E3 is an assertive enneagram as well. E8 is a bulldozer as 8w7. If you are an 8, you would be the more subdued 8w9. An 8w9 will be agreeable to a point- you cross their boundaries they bite. hard. While an 8w7 may fight to be dominant, an 8w9 is not as focused on being dominant but just doesn't want to be submissive. An 8w9 is considered more of an eruption than blunt anger like the 8w7 because 8w9 has a tendency to build up anger before eventually popping it in your face. I have a hard time seeing you as 8w7 at all because I've never seen you bulldoze somebody. I've seen you put out a very logical standbase like a good INTP and a 3, but you don't aim to crush your opposition...that I know of.
Sometimes E8 and E1 anger is hard to decipher between. So here's a mega pointer for you. E1 is the moralistic type, and they want to
convert you to their way of thinking. They do not crush you like an 8. They want to persuade you. I see you more like the E1 than the E8 because every time you made a debate of something, you are definitely merely trying to convince. I've never felt the air of hostility that exists in some 8s because they care little about persuasion. 8s are its my way or the highway people. Both can look to justice but E8 is more about in the moment stuff while E1s sit on these ideas constantly. In my opinion you would be a 1w9, merely because again never seen anything 2-like from you.
I honestly am not the best at instincts but I've always found you a little more Sp, than So. So I'd maybe go Sp/Sx rather than So.
Here's a sticker: AMBIEEEEE