cannot take screenshots in a banking app
This is a result of FLAG_SECURE. The reason is obviously again security - other apps can either leverage the native screenshot API, or just read your captured results from storage to potentially obtain sensitive info.

If you're already into Xposed framework, then there are a bunch of modules that will disable the check for the flag system-wide, such as this one.

As @iBug already pointed out, always exercise extreme caution when working around security measures, especially when a 3rd-party app is involved.