Reviving this, as I just bought a new 2024 and had the same issue. The middle seat has its buckle situated too far into the seat and has a metal base and hence is a rigid buckle. This makes it impossible for a child to put in the buckle when a booster is present.
Unfortunately, the buckle and tongue are of a non-standard model (TG-101) as well as different from non-standard models Ford used in other cars. As of today no extender exists.
Fortunately, the TG-101 differs only minorly from the standard tongue. It has a small gap to allow the buckle to distinguish and reject a normal tongue, as well as is wider at the top itself so it won't fit into a normal buckle. This as a normal buckle's plastic will not be wide enough.
All one needs to do is use metal grinder and make a small gap in a normal tongue, then open the plastic cap and widen the plastic insert a bit itself. The plastic cap's internal pins will likely break as it is not intended to be opened, but superglue will fix that - it is just the plastic cap. Possibly one can also widen the insert without opening the cap, e.g. with a small hand file, but I didn't have one small enough.
Nothing of these are in the structural parts of the extender and hence a safety concern. The strap, metal plate that holds the buckle as well as actual metal part that 'clicks' in the tongue are all untouched.
(Of course don't do this if yours are inflatable seatbelts.)
