My Garmin nuvi 40 does not work in my 2018 Crosstrek.What GPS can I use?

You need to figure out if the power outlet is working. Try plugging in something else in like a cell phone charger. If another device works then check the fuse for the outlet. It may not be your Garmin at all. Alex

Bear in mind the power outlet(s) requires key to be be on - they are not live with key off.