They can ask,and it’s not uncommon but also not standard. You can refuse but at least it’s a reasonable amount and they told you up front it was nonrefundable.
I’ve never paid a deposit and never had a lower value car, Volvo XC40, VW Tiguan R-Line and Skoda Enyaq 85x (all £2k+ APs) but possibly just lucky.
You aren’t tied to any one dealer so if you aren’t willing to pay in the future, just try ordering at a different dealer, you can still move back to your local for servicing etc.
I have always had the thought in my head that I’d refuse if asked but never actually had that idea tested.
"Man is born in freedom, but he soon becomes a slave, in cages of convention, from the cradle, to the grave."