Hi. Just wanted to add to this discussion, in case it helped anyone.
This AIB app is currently working for me on my Pixel 7a with the latest GrapheneOS build 2026090701.
I'm running Sandboxed Google Play in the owner profile. I had to download the app from Aurora store, as it won't show up in the Play Store.
Once downloaded, in the app setting, I've disabled "Secure app spawning". And under "Advanced" I've set "Play Integrity API" to blocked. This setup allows me to use the app fully. I get warnings when the app uses the integrity API, but the app still works. This setup also allowed me to get another banking (credit Union) app to work, that had previously not worked.
AIB app details are aib.ibank.android, version 26.8.45.
The fact that I'm blocking the integrity API feels a bit like I'm on a knife-edge, and it could fail with any update. But, for now, it's working.