[geekwithoutacause]

After a cold start I need to back out of my carport up a little hill. The car barely makes it up this hill in reverse. Engine does not rev up no matter how much throttle I give it. Seems to completely ignore more throttle. Doing the same driving forward up this hill when cold is no problem at all.
This is on a 2018 Forester XT. US model.
Currently has 4200 miles on it.

 

[Steel City Subi]

Confused...You mention XT and CVT???

 

[UhOh]

low power in reverse when cold ... Seems to completely ignore more throttle. Doing the same driving forward up this hill when cold is no problem at all.

doesn't explain your problem, but I've never driven right off from a cold start;
always have let car idle a bit (for >3 minutes in the winter).

 

[jzmtl]

XT has a very arbitrarily high reverse gear (even though CVT can do the full range forward or reverse), even fully warmed up it's a struggle to back up steep inclines. My guess is when engine is cold the ECU will not allow high revs or boost to protect the engine, coupled with the previously mentioned gear ratio problem is what you are seeing.