de0u Thanks for the data point. Is the Samsung device's OS at A14 QPR2? What is the build number?
Andreas PPR1.180610.011.G950FXXXUCDVI1
Hmm. I may be looking in the wrong place, but a search online turns up G950FXXUCDVI1 (two X's, not 3 X's) on this Samsung web page, listed as a release of Android 9 on 2022-09-21. If so, that is definitely not A14 QPR2, so the Millennium banking app working on that Android release would not shed light on whether or not the app runs on A14 QPR2.
If an app just stopped working when GrapheneOS was upgraded to A14 QPR2, and the app also stopped working on non-GrapheneOS Android devices that have been upgraded to A14 QPR2, then the problem likely isn't the GrapheneOS update, but instead that the app needs to be updated but hasn't been yet.
In the other direction, if the app is known to work on a non-GrapheneOS build of A14 QPR2 and doesn't work on GrapheneOS's A14 QPR2, then maybe there is an issue with the GrapheneOS update.