Google has discontinued and removed the both the iOS and Android AdSense apps since late 2019. For those of us who had the previously downloaded the app on our mobile devices, it still continued to work.
As of somewhere from the 16th to 17th August 2021, the app has finally stopped working on my iOS device. Data is no longer being received. This means that I'm no longer able to check my daily ad performance on the go. I also no longer get working access to my handle little AdSense widget that sits on my iPhone's Today's View. I surely enjoyed it while it lasted.
Google's decision to sunset the mobile apps was due to their change of focus to invest in the mobile web interface. This means that you should have an improved experience when using Google AdSense on mobile via http://www.google.com/adsense. You are able to check earnings on the go and run basic reports via the mobile web interface. However certain actions such as running custom reports and blocking ads are not available, and requires either using your desktop to access the web interface, or switching to the classic interface on mobile.