Here's a random suggestion - when I first got my Golf I set it up to use my mobile phone as a 2.4 GHz Wi-Fi hotspot to enable media streaming without having to pay for a data package. I soon changed my mind though as it stopped wireless Android Auto from working (as Wi-Fi needs to be enabled on the phone, which it isn't when you are using it as a hotspot). Then every time I started the car without the hotspot enabled on my phone, I got the 'media streaming unavailable' notification. I was able to clear this though permanently, by deleting the saved Wi-Fi connection from within the car Wi-Fi settings.
So, how about trying to setup the same to force the car to use a Wi-Fi hotspot rather than the inbuilt e-sim for media streaming. This *may* trick the car into forgetting that it use to use the sim for streaming. Then turn off the Wi-Fi hotspot on the phone, and delete the saved network from the car's Wi-Fi settings to clear the notification. Can't guarantee it'll work, but maybe worth a try?