A pic of the affected area would be a great help. Are the 2 floors running in parallel or at 90 deg.? Are the 2 floors level to each other?
Where they meet is not smooth. Not a clean edge.
If parallel and level you could run the oak up to it instead of a threshold.
If they're at butt ends are facing an interfacing material is the way to go. The floater floor will probably need to be occluded by the interface material to allow for expansion, the oak moves a little but if it's 5 or more yrs old it's done with most of its moving unless you're in a high moisture and heat area.
Wish I could be more help.
Never bite the hand that looks dirty!
The more you know the more you're worth