Eclat Cortex disassembly?

Probably the wrong flair, this one should have a question mark at the end, but bear with me🐻
And I don’t really need a piece of flair to express myself!
🖕🏼 Alright, this is my flair, okay?!
This is me – expressing – myself!

Sorry, got a bit carried away there..
Kudos to those that got the reference, but I actually came here to ask a (how to?) question..

I can’t -for the life of me- figure out how to take off the threaded nut that keeps the driver in place on my Éclat Cortex hub?
I want to open it and add another spacer to reduce slack, but even with a handheld vice and an allen key in the axle, it won’t move a millimetre (or a 32th of an inch for those in the US). I feel like the allen key is more likely to bend or snap before I’ll have any movement in the driver nut..🥴

Am I doing something wrong, or does anyone know a simple hack to open this thing up?

Pics for reference, tell me what I’m doing wrong or how to do it differently, please?
Thanks!