I don't know, it seems high to me. According to a CMG article ( Fast times with BMW’s R1200 GS Adventure | Canada Moto Guide )
a fully optioned one (like this one) in 2014 was $23,700 MSRP. I'm not sure how much BMW increased prices over the next 2 years.
It does have low km's but at some point it really doesn't matter that much.
I wouldn't compare it to a 2020 model as the changes are probably significant over the 4 years for a flagship model.
I agree with others; hard to view a $21K, 4 year old used bike as a bargain, but there's a buyer for everything I suppose.
$24k, plus $1k for the NavVI, plus $2k for OEM panniers, plus I think there are a couple extra packages like the quick shifter not quoted in that review.
It is what it is. I keep an eye on R1200GS(A) prices and this is about as cheap as I've seen one.