Laminate expansion gap at transition to extension?

Hello all,

I am hoping to lay some laminate in lounge, and continuing the flow through into my conservatory, however I am at a loss for what to do at the transition where the lounge flows into the conservatory (please see photo 1). I know I need an expansion gap, the question is how to do it. Please do not suggest scotia in front of the 'transition trim' (sorry I don't know what this is called) it has already been suggested and rejected!
From investigation (ie pulling back the carpet) that this was where a cavity wall used to be (please see picture two) however I am not sure what might lay underneath it. The bar itself appears to be an 'L' shape- with a lip (over a gap) facing into the existing part of the house, and a flat side (flush with the floor?) facing towards the conservatory extension.
My main question is, do you think it would be possible to undercut this board in the conservatory, to the the laminate expansion gap can be hidden this way? I guess that this is not needed in the lounge as the lip ought to do the same trick??
Thank you all in advance for your advice!!
The Mrs

Is there a reason you can't take it out ?

I've been a little hesitant to do this as
1) I am not sure how it would come out (any ideas) 2) I don't know what is underneath it(a larger gap, concrete? Again any ideas? And 3) the floor in the conservatory is lower than the original house (would this pose a problem?)
Many thanks again!
the Mrs

I'd lift it and make good underneath but if not...
use quickstep incizo doorbars on each side. Getting matching to the wood. On the board.
The trims can be made into T section profile and sit one on each side

thank you so much for your advice! Having a brand name to go for is very helpful! Will follow your advice!!