Alexa does have the XM Skill. It works fine for me, as long as there is cell connection.*A quick search finds links that indicate Alexa has an XM Radio skill.
Perhaps this, less than elegant process could be a "solution" for some?
That's also true, as far as I know. I don't have Bluetooth in my pickup, so I bought an Echo Auto from Amazon, along with a Bluetooth adapter to plug into a 12V outlet. It plays on the radio using the Alexa App from your phone. It works great with Spotify and Sirius XM, as long as you have cell connection. No doubt Rivian's Alexa will work way better than this $25 setup. I fully expect Rivian to have 3-month trials for each, Spotify, Sirius XM and Amazon Music. These also work on your other devices, computer, Echo Dots, Fire TV, etc.But an application would mean you’re using the SiriusXM stream off the internet, which means you need a cell connection. That defeats the entire advantage of SiriusXM over streaming services like Spotify for people who are often outside cell range.
My truck needed a transmission overhaul 3 weeks ago, (317,000 plus miles), so I had to buy a used vehicle (Thanks Rivian) for transportation while I waited for the repair. The used vehicle came with a 3-month trial of Sirius XM, plus an additional 3-months for $2.00. I'll just use the 3-month and won't subscribe to XM. I already have Spotify.