We are renovating a 40 year old, above grade condo in NC. After removing the carpet to prepare substrate for a floating bamboo floor, we discovered that along the inside of the sliding glass door leading out to the balcony, there is a crack along this area. The sliding glass door is framed by concrete That the metal door frame is set in and on. The crack occurs where the bottom of the concrete the door frame is set on should meet with the plywood substrate that runs along the outside half of this room.

I know an expansion area was left and with settling and temp change at that wide door, some of this was to be expected, but crack is wide enough at the top that some fix is needed. I have been told it is structurally sound and really have no doubt about this.
The flooring substrate along this half of the room is plywood raised above the plywood sub floor and was done this way so that when it meets the concrete substrate (on the side of the unit where any tiled areas might be put), both substrates would be even heights.The concrete substrate areas are 1''1/2'' concrete on top of the plywood sub floor with 2"x4"'s imbedded in the concrete where walls,doors, closets, rooms change, and extra points except where tile was specified. I was told that this was done to make concrete easier to pump in for 1 reason.Those concrete substrates are completely flat and uncracked after 40 years.

The question is, since this crack is wider than we can keep as it is for wood installation, we need to get a proper fix. Crack is wider at the top and narrows as it gets deeper(a V shape). There are no issues on the concrete balcony beyond.
I was informed this issue is usual for the above grade units here and most likely was a consideration that construction done this way to begin with. Is unusual to have half a room a raised plywood substrate.
I know that the crack should never be completely filled in, there always should be an expansion joint area honored and we were supposed to fill the edge with silicone caulk also.
Unless carpet was to remain (that is not an option), we need to find the most appropriate way to fix. I know this is type of issue that worries builders about structural issues but that has been well addressed and I am comfortable with that.
Knowing that still does not instruct us as to how and what to use to best address the issue so that all can be prepared to fill the gap and level so we can work with a proper installation of the flooring.The concrete base the doors is set on is more ragged underneath the area and something that bonds to concrete needs to be part of the fix as is ragged there but previously not noticeable.
I know over the years those dealing with older homes have seen everything. 40 year old, multifamily construction, with fire breaks may be a little different but I am sure not beyond you guys. Thanks