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The simpler solution from support actually worked. Thanks once more for providing insight to the problem, I was far more confident in what i was doing.

Very detailed explanation, thanks. Meanwhile SeeMe support did reply: Try heating the hotend up first, as if it came out, and the ptfe liner raised up to where the threads are, then it might not go back in if the hotend is cold Seems coherent with your ideas and much simpler, so I think I'll try ...

So, if I understood everything I should do the following: soak the nozzle heating it (will this suffice or should I make something else?) let it cool down :) unscrew the big bolt push down the small PTFE tube screw back the big bolt screw the brass fitting insert the bowden tube Am I correct? Thanks ...

I was thinking the same but... who knows? I mean: I had no idea what the open end should look like. Might it be that the PTFE bowden broke inside?
How am I supposed to remove it? Will I be able to find another bowden should it be too short now? I mean easily/cheaply as I'm from Europe (Italy)

Yes, the problem is with the brass fitting that seems impossible to thread in.
I cut the filament and examined the thread with a lens but it seems ok.
Here is a picture of the opposite side

My brass fitting unscrewd during a print. I stopped everything and tried to screw it again in place. It doesn't seem to fit anymore.
I would contact SeeMeCNC support but I already tried for a different problem and got no answer.
Any suggestion to fix my problem?

Thanks for replying to your answer, int2str. Your info was really useful for me. I received my Orion with the power supply set to 110V. A very bad idea for a shipment in Europe. Of course it was written in the manual, as I noticed 5' after burning the internal fuse. Is support from SeeMeCNC totally ...